* send ext.flutter.debugDumpApp; ext.flutter.reassemble

* expose debugDumpRenderTree

The new `empty_statements` lint (in the next DEV roll), flags these empty statements.  Harmless, except the one in `basic.dart` that fixes a real-life bug. :)

* send the reload source command for ios simulators

* review changes

* rewrite w/ a completer

* send supportsRestart flag when starting an app

* remove unused imports

* review comments

Fixes #4298

* show build progress; print app sizes

* add todo

* review comments

* remove unused import

* working on making a faster flutter run restart

* clean up todos; fire events on isolate changes

* use the Flutter.FrameworkInitialization event

* review comments

* iOS tools cleanup

1) Fix `flutter install` on both device and simulator to refer to the actual
   bundle and not just the .generated folder
2) Fix `flutter run` on device to actually run vs just installing

Still TODO:
1) Discovered that isAppInstalled on iOS simulator always reports true,
   meaning it'll never actually try to install the app.

Fixes #3947
Fixes #1823

Wire up ios-profile and ios-release. Switching between debug, profile and release starts the build process from scratch. (#4063)

This also fixes some related problems affecting "flutter run":
  * FLXes built during AndroidDevice.startApp need to match the build mode
  * APKs should always be rebuilt if the build mode uses AOT compilation

* rename service_protocol.dart to protocol_discovery.dart

* add a wrapper around the obs. protocol

* use json-rpc in run

* consolidate obs. code; implement flutter run --benchmark

* review comments

Artifacts from local engine builds will be found based on the --local-engine flag

Host tools can be found in the artifact cache directory for the host platform.
If a developer wants to use a local engine build instead, then provide an
--engine-build flag that selects the specific engine build variant.

* fix analysis errors

* review comments; fix test

* re-add an export for debugPrint

* rework flutter run

* fix npe with --debug-port

* connect to obs and exit when that conneciton closes

* update todos

* more terse flutter upgrade

* fix an issue when updating and the engine update code has changed

* call flutter precache; add a --no-color hidden option

* fix a lint related to getters/setters

Add a command that can capture a Skia picture of a Flutter frame and send it to a file or skiaserve debugger (#3165)

The .packages file is replacing the packages directory of symlinks.

All artifacts for iOS are universal.

The new name format is "DEVICE_TYPE_NAME (Flutter)". For example:

iPhone 6 (Flutter)
iPhone 6s Plus (Flutter)

The names are taken from `xcrun simctl list --json devicetypes`.

Fixes #2682