Fix comments from https://github.com/flutter/engine/pull/2721

I gave up before I was completely done.

Items still remaining include:

 * drawVertices
 * drawAtlas
 * TransferMode.*
 * VertexMode

Also:
 * Add a convenience constructor to RSTransform
 * Add some convenience methods to Rect and Size
 * Make some defaults more explicit

Tools can send a broadcast intent that will cause Flutter processes to
write their names and observatory ports to the log in JSON format.

* Update to mojo 7d579155cc597aa3befcbfad66eef54bda06b57c

* Update to new API

The Dart sources the pubspec are missing from the list of output paths. These artifacts can easily become stale.

Pre-populate the LOCAL_ENGINE xcconfig value so engine developers dont need to fill in different values. (#2716)

Pass the local-engine flag to both `build aot` and `build flx` to avoid using mismatched gen/sky_snapshot pairs. (#2715)

Previously we'd draw uninitialized memory. Now we draw black.

Fixes #3447

https://github.com/flutter/flutter/issues/4186

* Close the app after the user acknowledges the Launch Error alert.

Package map entries can contain relative paths, and these paths will be based
on the package map path as originally specified

Instead of trying to execute the script directly, use /bin/sh to execute the
script.

Switch sdk_xcode_harness to use flutter build aot

This patch moves a bunch of complexity out of FlutterApplication.xcodeproj and
into `flutter build aot`, which will make it easier for developers to create
their own FlutterApplication.xcodeproj.

This enables the specification of a local engine (via `--local-engine`)
for flutter tools to use.

* Create an Xcode project template for dynamic service creation.

The `create_native_service_sdk.py` will be run on the buildbot similar
to `create_ios_sdk.py`. This will create an Xcode project with both arm
and x64 assets that the user can use to fill in the service
implementation.

* Add the complete_static_lib property to sdk_lib_archive in
dynamic/BUILD.gn

It crashes. We either need to make it safe to call before
Dart_Initialize on Mac or we need to use some other way of measuring
startup time.

Fixes #4006

Update the flutter_gdb script to run on MacOS and make the engine build directory configurable (#2694)

Instead of depending on a potentially missing Interpreter.xcconfig, add the variable to Flutter.xcconfig. (#2689)

We still need this for the observatory build.

This reverts commit 5082974b.

The engine.git repo doesn't need a copy of the Dart SDK anymore.

Fixes https://github.com/flutter/flutter/issues/2618