* Enable Hot Reload on Windows (backed by gen_snapshot)

\o/

Two caveats:
* Hot Reload on Windows is slower than on other platforms because gen_snapshot is slower then sky_snapshot
* We currently cannot hot reload projects with spaces in the path

* enable tests

* improve the logger ui a bit for elapsed times

* invert param

* update daemon.dart

The zip files downloaded from cloud storage are not clearly separated
into engine artifacts and tools anyways.

Also, because of this unclear separation, we were downloading
`linux-x64/artifacts.zip` twice before.

...now that we have generic methods, their types need to be specified too.

* Update to Dart SDK `1.22.0-dev.6.0`.

* Update SDK summary generation to create spec and strong summaries.

* Updated to dev.8.0.

* Fixed console out.

This ensures that accidental usages of dart:io's
file API don't creep in over time.

This removes direct file access from within flutter_tools
in favor of using `package:file` via a `FileSystem` that's
accessed via the `ApplicationContext`.

This lays the groundwork for us to be able to easily swap
out the underlying file system when running Flutter tools,
which will be used to provide a record/replay file system,
analogous to what we have for process invocations.

- [x] Remove old benchmark code from the non-hot runner.
- [x] Remove some dead code.
- [x] Fix a throw that should be a rethrow.

* make showElapsedTime default to true

* support nested progresses

* improve hot reload message

* rethrow

These aren't needed anymore.

This rewrites imports of various mojom.dart files from the Flutter
engine repo to instead import normal-looking dart files from the
(new) flutter_services package. This package handles exporting the
correct symbols from generated code wherever that may live.

Includes an engine roll to 3551e7a48e2e336777b15c7637af92fd7605b6c5
which contains the new flutter_services package.

This will ensure cleanup of any files that existed in previous versions of
the artifacts but have since been removed

* Build sky_engine Dart SDK summary bundle on FlutterEngine.download().

* Tweaks for Devon comments.

* Tweaks for Phil comments.

* Add Dart SDK to version info (#4986).

Adds a new SDK line to the `flutter —version` output.

* Prefer `Platform.version`.

* Version text fixes.

We now download the base coverage file automatically.

This prevents multiple simultaneous runs of the analyzer from stomping
over each other (e.g. multiple runs of 'update-packages'). Certain
long-lived commands (like analyze, run, logs) are exempted once they've
done enough work to be safe from most stomping action.

This still doesn't make us entirely safe from craziness, e.g. if you're
half way through an 'update-packages' run and you call 'git pull', who
knows what state you'll end up in. But there's only so much one can do.

Fixes https://github.com/flutter/flutter/issues/2762

Instead of embedding Flutter.framework and BuildFlutterApp in the Xcode
project, we store these in flutter.git, where we can reference them.

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

* 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