Issue 1:
This may possibly be due to OOM on LTO builds. Example: https://uberchromegw.corp.google.com/i/client.flutter/builders/Mac%20Engine/builds/2002/steps/build%20host_debug/logs/stdio

Issue 2:
Macbot flaked during the build ios flutter_gallery step.

Relevant log section:

Ld /b/build/slave/Mac/build/flutter/examples/flutter_gallery/build/ios/Release-iphoneos/url_launcher/url_launcher.framework/url_launcher normal arm64
cd /b/build/slave/Mac/build/flutter/examples/flutter_gallery/ios/Pods
export IPHONEOS_DEPLOYMENT_TARGET=8.0
export PATH="/Applications/Xcode9.0.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin:/Applications/Xcode9.0.app/Contents/Developer/usr/bin:/b/build/slave/Mac/build/flutter/bin:/b/build/slave/Mac/build/flutter/bin/cache/dart-sdk/bin:/b/build/slave/Mac/build/flutter/dev/bots/gradle/gradle-2.14.1/bin:/b/cipd_path_tools:/b/cipd_path_tools/bin:/b/cipd_client:/Users/chrome-bot/slavebin:/b/depot_tools:/usr/local/git/bin:/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin"
/Applications/Xcode9.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -arch arm64 -dynamiclib -isysroot /Applications/Xcode9.0.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS11.0.sdk -L/b/build/slave/Mac/build/flutter/examples/flutter_gallery/build/ios/Release-iphoneos/url_launcher -F/b/build/slave/Mac/build/flutter/examples/flutter_gallery/build/ios/Release-iphoneos/url_launcher -F/b/build/slave/Mac/build/flutter/examples/flutter_gallery/ios/Pods/../../../../bin/cache/artifacts/engine/ios-release -filelist /Users/chrome-bot/Library/Developer/Xcode/DerivedData/Runner-gpxpofezffwfvidmsobfnwkndufp/Build/Intermediates.noindex/Pods.build/Release-iphoneos/url_launcher.build/Objects-normal/arm64/url_launcher.LinkFileList -install_name @rpath/url_launcher.framework/url_launcher -Xlinker -rpath -Xlinker @executable_path/Frameworks -Xlinker -rpath -Xlinker @loader_path/Frameworks -miphoneos-version-min=8.0 -dead_strip -Xlinker -object_path_lto -Xlinker /Users/chrome-bot/Library/Developer/Xcode/DerivedData/Runner-gpxpofezffwfvidmsobfnwkndufp/Build/Intermediates.noindex/Pods.build/Release-iphoneos/url_launcher.build/Objects-normal/arm64/url_launcher_lto.o -fobjc-arc -fobjc-link-runtime -framework Flutter -framework Foundation -single_module -compatibility_version 1 -current_version 1 -Xlinker -dependency_info -Xlinker /Users/chrome-bot/Library/Developer/Xcode/DerivedData/Runner-gpxpofezffwfvidmsobfnwkndufp/Build/Intermediates.noindex/Pods.build/Release-iphoneos/url_launcher.build/Objects-normal/arm64/url_launcher_dependency_info.dat -o /b/build/slave/Mac/build/flutter/examples/flutter_gallery/build/ios/Release-iphoneos/url_launcher/url_launcher.framework/url_launcher

GenerateDSYMFile /b/build/slave/Mac/build/flutter/examples/flutter_gallery/build/ios/Release-iphoneos/url_launcher/url_launcher.framework.dSYM /b/build/slave/Mac/build/flutter/examples/flutter_gallery/build/ios/Release-iphoneos/url_launcher/url_launcher.framework/url_launcher
cd /b/build/slave/Mac/build/flutter/examples/flutter_gallery/ios/Pods
export PATH="/Applications/Xcode9.0.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin:/Applications/Xcode9.0.app/Contents/Developer/usr/bin:/b/build/slave/Mac/build/flutter/bin:/b/build/slave/Mac/build/flutter/bin/cache/dart-sdk/bin:/b/build/slave/Mac/build/flutter/dev/bots/gradle/gradle-2.14.1/bin:/b/cipd_path_tools:/b/cipd_path_tools/bin:/b/cipd_client:/Users/chrome-bot/slavebin:/b/depot_tools:/usr/local/git/bin:/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin"
/Applications/Xcode9.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/dsymutil /b/build/slave/Mac/build/flutter/examples/flutter_gallery/build/ios/Release-iphoneos/url_launcher/url_launcher.framework/url_launcher -o /b/build/slave/Mac/build/flutter/examples/flutter_gallery/build/ios/Release-iphoneos/url_launcher/url_launcher.framework.dSYM
Command /Applications/Xcode9.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/dsymutil failed with exit code 11

** BUILD FAILED **