Issue 1:
As reported by someone who tried this yesterday on Android. Confirmed on both Android N and Android O.

This was the chunk of code that when added, lead to the exception:

// Modify the _buildTextComposer method with the code below to define the
// send button.

// ...
new Container( //new
margin: new EdgeInsets.symmetric(horizontal: 4.0), //new
child: new IconButton( //new
icon: new Icon(Icons.send),
onPressed: () => _handleSubmitted(_textController.text)),//new
),

After this step in the codelab, the user can type into the text field, but when they hit the arrow button, they get this exception:

here's the log from adb logcat from Android N 7.1.2:

06-16 15:09:41.380 29675 29751 W GAv4 : Discarding hit. Too many hits sent too quickly, rate limiting invoked: sr=1080x1794,sf=100.0,ec=sync,ev=0,cid=6aeba2c7-3c46-492c-91a4-e84f0b5e5dae,_v=ma10.2.98,av=1.7.232.05.40,aip=1,v=1,a=1129632470,an=Slides,ul=en-us,t=event,tid=UA-21125203-7,aiid=com.android.vending,ea=entriesChanged,aid=com.google.android.apps.docs.editors.slides,el=null
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput: Failed to handle method call
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput: java.lang.IndexOutOfBoundsException: setSpan (-1 ... -1) starts before 0
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at android.text.SpannableStringBuilder.checkRange(SpannableStringBuilder.java:1325)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at android.text.SpannableStringBuilder.setSpan(SpannableStringBuilder.java:683)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at android.text.SpannableStringBuilder.setSpan(SpannableStringBuilder.java:676)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at android.text.Selection.setSelection(Selection.java:76)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at io.flutter.plugin.editing.TextInputPlugin.setTextInputEditingState(TextInputPlugin.java:147)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at io.flutter.plugin.editing.TextInputPlugin.onMethodCall(TextInputPlugin.java:66)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:191)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at io.flutter.view.FlutterView.handlePlatformMessage(FlutterView.java:643)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at android.os.MessageQueue.nativePollOnce(Native Method)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at android.os.MessageQueue.next(MessageQueue.java:323)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at android.os.Looper.loop(Looper.java:136)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at android.app.ActivityThread.main(ActivityThread.java:6121)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at java.lang.reflect.Method.invoke(Native Method)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)
06-16 15:09:42.255 29524 29524 E MethodChannel#flutter/textinput:	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)
06-16 15:09:42.277 29524 29544 I flutter : ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
06-16 15:09:42.295 29524 29544 I flutter : The following assertion was thrown during paint():
06-16 15:09:42.295 29524 29544 I flutter : 'package:flutter/src/rendering/object.dart': Failed assertion: line 2110: 'owner == null ||
06-16 15:09:42.295 29524 29544 I flutter : !owner.debugDoingPaint': is not true.
06-16 15:09:42.302 29524 29544 I flutter :
06-16 15:09:42.302 29524 29544 I flutter : Either the assertion indicates an error in the framework itself, or we should provide substantially
06-16 15:09:42.302 29524 29544 I flutter : more information in this error message to help you determine and fix the underlying cause.
06-16 15:09:42.303 29524 29544 I flutter : In either case, please report this assertion by filing a bug on GitHub:
06-16 15:09:42.303 29524 29544 I flutter : https://github.com/flutter/flutter/issues/new
06-16 15:09:42.303 29524 29544 I flutter :
06-16 15:09:42.303 29524 29544 I flutter : When the exception was thrown, this was the stack:
06-16 15:09:42.311 29524 29544 I flutter : #2 RenderObject.markNeedsPaint (package:flutter/src/rendering/object.dart:2110)
06-16 15:09:42.312 29524 29544 I flutter : #3 _RenderInkFeatures._didChangeLayout (package:flutter/src/material/material.dart:315)
06-16 15:09:42.312 29524 29544 I flutter : #4 _MaterialState.build.<anonymous closure> (package:flutter/src/material/material.dart:228)
06-16 15:09:42.312 29524 29544 I flutter : #5 NotificationListener._dispatch (package:flutter/src/widgets/notification_listener.dart:110)
06-16 15:09:42.312 29524 29544 I flutter : #6 Notification.visitAncestor (package:flutter/src/widgets/notification_listener.dart:43)
06-16 15:09:42.312 29524 29544 I flutter : #7 LayoutChangedNotification&ViewportNotificationMixin.visitAncestor (package:flutter/src/widgets/scroll_notification.dart:36)
06-16 15:09:42.312 29524 29544 I flutter : #8 Element.visitAncestorElements (package:flutter/src/widgets/framework.dart:3103)
06-16 15:09:42.312 29524 29544 I flutter : #9 Notification.dispatch (package:flutter/src/widgets/notification_listener.dart:57)
06-16 15:09:42.312 29524 29544 I flutter : #10 ScrollActivity.dispatchScrollStartNotification (package:flutter/src/widgets/scroll_activity.dart:90)
06-16 15:09:42.312 29524 29544 I flutter : #11 ScrollPosition.didStartScroll (package:flutter/src/widgets/scroll_position.dart:543)
06-16 15:09:42.312 29524 29544 I flutter : #12 ScrollPosition.beginActivity (package:flutter/src/widgets/scroll_position.dart:535)
06-16 15:09:42.312 29524 29544 I flutter : #13 ScrollPositionWithSingleContext.beginActivity (package:flutter/src/widgets/scroll_position_with_single_context.dart:119)
06-16 15:09:42.312 29524 29544 I flutter : #14 ScrollPositionWithSingleContext.animateTo (package:flutter/src/widgets/scroll_position_with_single_context.dart:186)
06-16 15:09:42.312 29524 29544 I flutter : #15 ScrollController.animateTo (package:flutter/src/widgets/scroll_controller.dart:143)
06-16 15:09:42.312 29524 29544 I flutter : #16 EditableTextState._handleCaretChanged (package:flutter/src/widgets/editable_text.dart:463)
06-16 15:09:42.312 29524 29544 I flutter : #17 RenderEditable._paintCaret (package:flutter/src/rendering/editable.dart:497)
06-16 15:09:42.312 29524 29544 I flutter : #18 RenderEditable._paintContents (package:flutter/src/rendering/editable.dart:515)
06-16 15:09:42.312 29524 29544 I flutter : #19 RenderEditable.paint (package:flutter/src/rendering/editable.dart:531)
06-16 15:09:42.312 29524 29544 I flutter : #20 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2259)
06-16 15:09:42.313 29524 29544 I flutter : #21 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:116)
06-16 15:09:42.313 29524 29544 I flutter : #22 RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:123)
06-16 15:09:42.313 29524 29544 I flutter : #23 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2259)
06-16 15:09:42.313 29524 29544 I flutter : #24 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:116)
06-16 15:09:42.313 29524 29544 I flutter : #25 RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:123)
06-16 15:09:42.313 29524 29544 I flutter : #26 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2259)
06-16 15:09:42.313 29524 29544 I flutter : #27 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:116)
06-16 15:09:42.313 29524 29544 I flutter : #28 RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:123)
06-16 15:09:42.313 29524 29544 I flutter : #29 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2259)
06-16 15:09:42.313 29524 29544 I flutter : #30 PaintingContext.paintChild (package:flutter/src/rendering/object.dart:116)
06-16 15:09:42.313 29524 29544 I flutter : #31 RenderBox&RenderObjectWithChildMixin&RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:123)
06-16 15:09:42.313 29524 29544 I flutter : #32 RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2259)
06-16 15:09:42.313 29524 29544 I flutter : #33 PaintingContext.repaintCompositedChild (package:flutter/src/rendering/object.dart:96)
06-16 15:09:42.313 29524 29544 I flutter : #34 PipelineOwner.flushPaint (package:flutter/src/rendering/object.dart:1085)
06-16 15:09:42.313 29524 29544 I flutter : #35 BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:253)
06-16 15:09:42.313 29524 29544 I flutter : #36 BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:504)
06-16 15:09:42.313 29524 29544 I flutter : #37 BindingBase&SchedulerBinding&GestureBinding&ServicesBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:189)
06-16 15:09:42.314 29524 29544 I flutter : #38 BindingBase&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:688)
06-16 15:09:42.314 29524 29544 I flutter : #39 BindingBase&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:636)
06-16 15:09:42.314 29524 29544 I flutter : #40 _drawFrame (file:///b/build/slave/Linux_Engine/build/src/flutter/lib/ui/hooks.dart:70)
06-16 15:09:42.314 29524 29544 I flutter : (elided 2 frames from class _AssertionError)
06-16 15:09:42.334 29524 29544 I flutter :
06-16 15:09:42.334 29524 29544 I flutter : The following RenderObject was being processed when the exception was fired:
06-16 15:09:42.334 29524 29544 I flutter : RenderEditable#1023788513 relayoutBoundary=up14
06-16 15:09:42.334 29524 29544 I flutter : creator: _Editable ← _ScrollableScope ← IgnorePointer-[GlobalKey#548512129] ← Listener ←
06-16 15:09:42.334 29524 29544 I flutter : _GestureSemantics ← RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#404540233] ←
06-16 15:09:42.334 29524 29544 I flutter : RepaintBoundary ← CustomPaint ← RepaintBoundary ← NotificationListener<ScrollNotification> ←
06-16 15:09:42.334 29524 29544 I flutter : GlowingOverscrollIndicator ← Scrollable ← ⋯
06-16 15:09:42.334 29524 29544 I flutter : parentData: <none> (can use size)
06-16 15:09:42.334 29524 29544 I flutter : constraints: BoxConstraints(w=339.4, 0.0<=h<=321.1)
06-16 15:09:42.334 29524 29544 I flutter : size: Size(339.4, 38.0)
06-16 15:09:42.334 29524 29544 I flutter : cursorColor: Color(0xff90caf9)
06-16 15:09:42.334 29524 29544 I flutter : showCursor: ValueNotifier<bool>#369763540(true)
06-16 15:09:42.334 29524 29544 I flutter : maxLines: 2
06-16 15:09:42.334 29524 29544 I flutter : selectionColor: Color(0xff90caf9)
06-16 15:09:42.334 29524 29544 I flutter : textScaleFactor: 1.0
06-16 15:09:42.334 29524 29544 I flutter : selection: TextSelection(baseOffset: -1, extentOffset: -1, affinity: TextAffinity.downstream,
06-16 15:09:42.334 29524 29544 I flutter : isDirectional: false)
06-16 15:09:42.334 29524 29544 I flutter : offset: ScrollPositionWithSingleContext#309474994(offset: 0.0, range: 0.0..0.0, viewport: 38.0,
06-16 15:09:42.334 29524 29544 I flutter : ScrollableState, ClampingScrollPhysics -> ClampingScrollPhysics,
06-16 15:09:42.334 29524 29544 I flutter : DrivenScrollActivity#359018454(AnimationController#111705517(▶ 0.000; for DrivenScrollActivity)),
06-16 15:09:42.334 29524 29544 I flutter : ScrollDirection.idle)
06-16 15:09:42.334 29524 29544 I flutter : This RenderObject has no descendants.
06-16 15:09:42.334 29524 29544 I flutter : ════════════════════════════════════════════════════════════════════════════════════════════════════
06-16 15:09:42.345 29524 29544 E flutter : [ERROR:../../lib/tonic/logging/dart_error.cc(16)] Unhandled exception:
06-16 15:09:42.345 29524 29544 E flutter : PlatformException(error, setSpan (-1 ... -1) starts before 0, null)
06-16 15:09:42.345 29524 29544 E flutter : #0 JSONMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:145)
06-16 15:09:42.345 29524 29544 E flutter : #1 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:154)
06-16 15:09:42.345 29524 29544 E flutter : <asynchronous suspension>
06-16 15:09:42.345 29524 29544 E flutter : #2 OptionalMethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:228)
06-16 15:09:42.345 29524 29544 E flutter : <asynchronous suspension>
06-16 15:09:42.345 29524 29544 E flutter : #3 TextInputConnection.setEditingState (package:flutter/src/services/text_input.dart:248)
06-16 15:09:42.345 29524 29544 E flutter : #4 EditableTextState._updateRemoteEditingValueIfNeeded (package:flutter/src/widgets/editable_text.dart:342)
06-16 15:09:42.345 29524 29544 E flutter : #5 EditableTextState._didChangeTextEditingValue (package:flutter/src/widgets/editable_text.dart:516)
06-16 15:09:42.345 29524 29544 E flutter : #6 ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:129)
06-16 15:09:42.345 29524 29544 E flutter : #7 ValueNotifier.value= (package:flutter/src/foundation/change_notifier.dart:184)
06-16 15:09:42.345 29524 29544 E flutter : #8 TextEditingController.clear (package:flutter/src/widgets/editable_text.dart:95)
06-16 15:09:42.345 29524 29544 E flutter : #9 ChatScreenState._handleSubmitted (file:///Users/nasir/flutter-work/my_friendlychat/lib/main.dart:67)
06-16 15:09:42.345 29524 29544 E flutter : #10 ChatScreenState._buildTextComposer.<anonymous closure> (file:///Users/nasir/flutter-work/my_friendlychat/lib/main.dart:58)
06-16 15:09:42.345 29524 29544 E flutter : #11 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:229)
06-16 15:09:42.345 29524 29544 E flutter : #12 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:67)
06-16 15:09:42.345 29524 29544 E flutter : #13 TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:149)
06-16 15:09:42.345 29524 29544 E flutter : #14 TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:92)
06-16 15:09:42.345 29524 29544 E flutter : #15 PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:268)
06-16 15:09:42.345 29524 29544 E flutter : #16 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:73)
06-16 15:09:42.345 29524 29544 E flutter : #17 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101)
06-16 15:09:42.345 29524 29544 E flutter : #18 BindingBase&SchedulerBinding&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:127)
06-16 15:09:42.345 29524 29544 E flutter : #19 BindingBase&SchedulerBinding&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:105)
06-16 15:09:42.345 29524 29544 E flutter : #20 BindingBase&SchedulerBinding&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:86)
06-16 15:09:42.345 29524 29544 E flutter : #21 BindingBase&SchedulerBinding&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:45)
06-16 15:09:42.345 29524 29544 E flutter : #22 BindingBase&SchedulerBinding&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:38)
06-16 15:09:42.345 29524 29544 E flutter : #23 _dispatchPointerDataPacket (file:///b/build/slave/Linux_Engine/build/src/flutter/lib/ui/hooks.dart:55)
06-16 15:09:44.684 1058 1068 I art : Background sticky concurrent mark sweep GC freed 71424(4MB) AllocSpace objects, 42(4MB) LOS objects, 14% free, 50MB/59MB, paused 2.829ms total 102.627ms
06-16 15:09:44.862 29675 29874 W JSVM : JSVM cleanup: hasContext=true, isCleaned=false

Issue 2:
I hit it first after making minor changes to the flutter code lab, and am hitting it now, while trying to put together a simpler flutter app.

Hot reload is not working, cold launches sometimes work.

Flutter run from IJ.

Launching lib/main.dart on Nexus 6P in debug mode...

Built build/app/outputs/apk/app-debug.apk (21.7MB).

W/IInputConnectionWrapper(21208): reportFullscreenMode on inexistent InputConnection

I/flutter (21208): executeQuery

Restarted app in 1,286ms.

E/MethodChannel#flutter/textinput(21208): Failed to handle method call

E/MethodChannel#flutter/textinput(21208): java.lang.IndexOutOfBoundsException: setSpan (-1 ... -1) starts before 0

E/MethodChannel#flutter/textinput(21208):	at android.text.SpannableStringBuilder.checkRange(SpannableStringBuilder.java:1325)

E/MethodChannel#flutter/textinput(21208):	at android.text.SpannableStringBuilder.setSpan(SpannableStringBuilder.java:683)

E/MethodChannel#flutter/textinput(21208):	at android.text.SpannableStringBuilder.setSpan(SpannableStringBuilder.java:676)

E/MethodChannel#flutter/textinput(21208):	at android.text.Selection.setSelection(Selection.java:76)

E/MethodChannel#flutter/textinput(21208):	at io.flutter.plugin.editing.TextInputPlugin.setTextInputEditingState(TextInputPlugin.java:147)

E/MethodChannel#flutter/textinput(21208):	at io.flutter.plugin.editing.TextInputPlugin.onMethodCall(TextInputPlugin.java:66)

E/MethodChannel#flutter/textinput(21208):	at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:191)

E/MethodChannel#flutter/textinput(21208):	at io.flutter.view.FlutterView.handlePlatformMessage(FlutterView.java:643)

E/MethodChannel#flutter/textinput(21208):	at android.os.MessageQueue.nativePollOnce(Native Method)

E/MethodChannel#flutter/textinput(21208):	at android.os.MessageQueue.next(MessageQueue.java:323)

E/MethodChannel#flutter/textinput(21208):	at android.os.Looper.loop(Looper.java:136)

E/MethodChannel#flutter/textinput(21208):	at android.app.ActivityThread.main(ActivityThread.java:6121)

E/MethodChannel#flutter/textinput(21208):	at java.lang.reflect.Method.invoke(Native Method)

E/MethodChannel#flutter/textinput(21208):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)

E/MethodChannel#flutter/textinput(21208):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)

flutter analyze:

~/src/github/flutter/bin/flutter analyze

Analyzing jwren/src/github/flutter_google_knowledge_graph...

hint • The value of the local variable 'v' isn't used at lib/main.dart:97:9 • unused_local_variable

1 issue found.

(Ran in 4.5s)