Switch from hack_load_vm_file_hook to PlatformPlugin

Atom validation

refactor the stop command to not use DeviceStore

Add DismissDirection onDismissed() callback parameter

refactor to move an ios specific class out of globals.dart

Don't install the Cloud SDK on Travis

This patch switches us from using our previous hacking approach to integrating
with package:test to using the new PlatformPlugin interface.

Add a test for icon opacity crash

Add type parameters to uses of PopupMenuItem

We don't need this anymore.

Fixes #2361

Update engine.version

This test causes the buildbot to hang. We don't currently have any hang
protection, which means this test ends up killing the bot. Disable the
test for now why we work on the root issues.

[driver] serialize commands to plain strings

Update engine

This change brings in a new version of Mojo, which has improved Mozart
interfaces.

Turns out VM service only accepts flat parameter name/value pairs. It
only worked this far because vm_service_client (mistakenly) uses JSON
encoder to encode parameters.

This change separates the Command type hierarchy from that of Result and
tightens type constraints on Command object parameters.

driver.scroll action; scroll perf test for Stocks

[driver] wait for the isolate to enter pause on start

Fix Icon opacity handling

Use bilinear interpolation when scaling images

Fixes #2337

Restore scrolled tabs support 

move the link around for flutter doc homepage

Hide icons in the accessibility tree.

Add "form" parameter to AnimationController forward and reverse

iOS Simulator: Attempt 'sideloading' the updated Flutter application if the application runner is already up