Repository: flutter
Issue: Strange Shape Behavior when trying to implement Speed dial Transition with FAB
Labels: framework,f: material design,a: quality,has reproducible steps,P3,found in release: 3.3,found in release: 3.6,team-design,triaged-design

Hey,

I was trying to develop FAB with Speed dial, but I've encountered problem presented below.
It is visible only for centerDocked and endDocked floatingActionButtonLocation.
I've minimized my code, to present the behaviour.
When you change the container height, then the shape is different. It was also clearly visible when BottomAppBar had childs.


## Steps to Reproduce

**Code:**
```
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MainScreen(),
    );
  }
}

class MainScreen extends StatefulWidget {
  @override
  _MainScreenState createState() => _MainScreenState();
}

class _MainScreenState extends State<MainScreen> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(child: Text('Text')),
      extendBody: true,
      bottomNavigationBar: BottomAppBar(
        color: Colors.black,
        shape: CircularNotchedRectangle(),
      ),
      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
      floatingActionButton: Container(
        height: 300.0,
        child: FloatingActionButton(
          child: Icon(Icons.add),
          onPressed: () {},
        ),
      )
    );
  }
}
```

**Screenshot:**
![obraz](https://user-images.githubusercontent.com/29212281/63892637-670cd280-c9e8-11e9-819a-96ce693e2564.png)



flutter doctor -v
```
[√] Flutter (Channel stable, v1.7.8+hotfix.4, on Microsoft Windows [Version 10.0.17134.950], locale en-US)
    • Flutter version 1.7.8+hotfix.4 at C:\Flutter
    • Framework revision 20e59316b8 (6 weeks ago), 2019-07-18 20:04:33 -0700
    • Engine revision fee001c93f
    • Dart version 2.4.0


[√] Android toolchain - develop for Android devices (Android SDK version 29.0.0)
    • Android SDK at C:\Users\bogat\AppData\Local\Android\sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 29.0.0
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)
    • All Android licenses accepted.

[√] Android Studio (version 3.5)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 38.2.3
    • Dart plugin version 191.8423
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b03)

[√] VS Code (version 1.37.1)
    • VS Code at C:\Users\bogat\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.3.0

[√] Connected device (1 available)
    • Android SDK built for x86 • emulator-5554 • android-x86 • Android 9 (API 28) (emulator)

• No issues found!
```