30+4 has made some changes to the remoting protocol that are incompatbile
with a test harness running 30+3 (e.g. adding a type='initial' field to the
first message)

* Use engine-built dart sdk

* Download dart-sdk from engine

* Move up deps to fix dart sdk constraint problem

* Update update_dart_sdk.ps1 for Windows

* Fix tests so they pass analysis

* More types for tests

* Roll engine

* Update dart sdk stamp location in flutter.bat

* Add newline

We need to pull in Dart 2 compliant mockito

Fixes #14532

There were some problems I introduced with the last PR for this. It passed the test, but failed in practice.

This adds tests for those failure cases, adds a "--help" and fixes the test so that it doesn't try and actually download MinGit as part of the Windows test.

I added package:platform as a dependency, so I did a force upgrade on the packages.

Also, re-enabling 'create package' in the cache warming code, now that #14448 is fixed.

* Unpin package:test and upgrade packages

* Update packages/flutter/test/foundation/stack_trace_test.dart

* Also add packages/flutter_tools/test/data/asset_test/font/.dartignore to ensure that update-packages --force-upgrade does not crash.

Rolling the Dart SDK to 2.0, with associated package updates.  

https://groups.google.com/forum/#!topic/flutter-dev/E22RdKAYjs8

* Revert "Reverting package changes until I can figure out how to fix Windows. (#14007)"

This reverts commit 6fda8ee8.

* Make prepare_package run on Windows

* Revert "Fixed output validation. (#14005)"

This reverts commit d84398db.

* Revert "Update package prep script to do async process execution and emit output as it happens. (#13918)"

This reverts commit b7169c1d.

 - Switches to async process execution, which now shows output as it happens instead of in chunks when the process completes
-  Now uses ProcessManager so that it may be mocked for the test.
- Adds in the download and install of mingit on Windows.
- Updated package dependencies because of added dependency on process package.

This simply updates the package dependencies by running flutter update-packages --force-upgrade.

I'm doing this with no other changes, because the last time I tried that, redness occurred. I want to isolate the problem to a "clean" update of the packages.

It looks like the plugins device_info, connectivity, and url_launcher haven't yet had their gradle configurations updated, so they fail when trying to build with the new gradle. I did not upgrade for those three packages only (in flutter_gallery) until we are ready to fix them (fixing them for master will break them for alpha users, so we need to do an alpha roll to do that).

This reverts commit 765191e7.
because the updated packages cause a gradle build problem.

This adds our self-compiled copy of the MinGit executable (built from the flutter/git repo) to the archive when building an archive for Windows.

I also tweaked the internal API for prepare_package.dart so that there's a single entry point to build an archive.

* flutter update-packages

* update plugin registrant for flutter_gallery