After the refactoring of the animation library, we were missing some
dartdoc.

Bump the dart version used on the infra bots to 1.14.1

Refactor flx.build() to allow for external toolchain hooks.

Otherwise the analyzer blows up.

@abarth

This splits flx.build() into two methods, flx.build() and
flx.assemble().  builD() now does the following:
1) constructs the manifest map by reading the manifest from the
   file system
2) "compiles" the dart code into the snapshot file
3) Invokes assemble()

This allows external build toolchains to construct their own
manifest map (possibly using a different manifest syntax)
and create their own snapshot file

Add a download_dart_sdk.py script for infra bots

remove no longer needed code from the service protocol extensions

@abarth

get the adb device name when using the adb server

remove an extraneous line of output when launching the simulator

Flutter sprites test

Fixed a typo.

Added the FAB per Tab demo

Demonstrates that when the Scaffold's Floating Action Button is changed, the new one (if any) fades and turns in.

Similar to the "Lateral Screens" demo here https://www.google.com/design/spec/components/buttons-floating-action-button.html#buttons-floating-action-button-behavior

There are more tabs and different tab views to demo more kinds of FAB changes.

add test for ModalBarrier

better error message when Navigator is used with no NavigatorState in…

Added a flexible appbar gallery demo

Added a "Patterns/Scrolling Techniques" demo that resembles the "Flexible Space with Image" from the Material design spec - https://www.google.com/design/spec/patterns/scrolling-techniques.html#scrolling-techniques-scrolling

Demos for the other app bar arrangements are still needed.

transformPoint should use Matrix4.perspectiveTransform

We want to normalize by w.

Fixes #1585

Adds initial version of weather to the gallery app

rev engine

Initial work to add Mozart child views

'flutter start' calls 'flutter apk' if necessary.

Fix formatting on AssetVendor's dart doc

flutter start no longer depends on a pre-built SkyShell.apk. It builds a
new one, as long as an AndroidManifest.xml exists.

We rebuild the .apk every time either AndroidManifest.xml or
flutter.yaml changes.

normalize -t --target option

Move ServiceMocker into flutter_test

People writing their own tests will want to mock services as well.

Update flutter_sprites now that ImageResource.first returns an ImageInfo

Actually return a SemanticsServer service.