Add a `flutter upgrade` command

This command upgrades the version of flutter that you're using and runs
`pub upgrade` to update the transitive dependencies.

showSnackBar() returns a Future, clears its placeholder

The returned Future completes after the snack bar has been dismissed.

Revised BottomSheet to ensure that its Future only runs after the bottom sheet has been dismissed.

TransitionRoute completer is now optional.

also listen for flutter in the adb logs

update double tap reference

service_registry.dart should use the service registry handle instead of shell handle

Fixes assert connecting to Activity service under Linux

Update the interactive_flex example for the new event handlers

shell handle.

R=@abarth,@tonygentilcore

Fixes #313.

Add a persistent bottom sheet to the stocks demo

Move data out of Github and into Firebase

@abarth @collinjackson

Fix adb parse

Update to match Hixie's changed bash script

Adding windows batch file to complement the bash script.

Raw keyboard example

Update the raw examples to handle PointerPacket events

Give loose contraints to text inside input widget

Named parameters for the mock_events.dart TestPointer class

The input widget scrolls, so it should give its text loose constraints.  That
way the text ends up being its intrinsic size even if put in a context with
tight constraints.

Fixes #298

Add a unit test for persistent bottom sheets

ShowBottomSheet now clears its placeholder after the bottom sheet has been dismissed.

Added support for generating fling gestures to WidgetTester.

Receive pointer events through PointerPackets

Fix remaining analyzer warnings