Previously, we would show 4 progress bars, which made it very unclear
what was going on since we'd just said "downloading engine". Now each
separate thing we download has its own announcement.

Eventually we should probably only download Dart, then do the rest of
this inside the flutter tool, as necessary.

Added support for Dismissable leave-behind list items

remove the _embedder.yaml file

implement --watch for flutter analyze

Cleanup around viewports

Cleanup build

Improve message when target not found

SizeObserver crusade: Remove SizeObserver

https://github.com/flutter/flutter/issues/2368

Include more details in the Red Box of Doom

Synchronizes dartdoc with dart:ui

Mostly just adds some examples to match the examples with use for
similar concepts in dart:ui.

Remove the second argument to WidgetError.

Remove the second argument to MultiChildLayoutDelegate.performLayout()

Fixes https://github.com/flutter/flutter/issues/2403

I have an e-mail ready to send to flutter-dev about this.

This makes WidgetError more like RenderingError, which will aid with https://github.com/flutter/flutter/issues/2356.

Fixes https://github.com/flutter/flutter/issues/2443

Factor out non-Material parts of MaterialApp into WidgetsApp

Remove Simulatable and restyle simulation_group.dart

Clarify the assert when mimicking twice in a row.

Fixes https://github.com/flutter/flutter/issues/1346

Try to clarify that you need a Material for an IconButton.

Flinging continuously should have one scroll start/end pair

Previously we got confused and started sending start/end pairs for each tick of
the fling animation.

Fixes #2430

Some more dartdoc

Fixes https://github.com/flutter/flutter/issues/2369

Clarify the "needs an Overlay" assert.

fix flutter create

Fixes https://github.com/flutter/flutter/issues/2436

[infra] run recipes using recommended method