Fixes https://github.com/flutter/flutter/issues/5588

* implement flutter packages get/upgrade command
* alias flutter pub
* refactor findProjectRoot for use by multiple commands

fixes https://github.com/flutter/flutter/issues/4994

This change adds a top-level getBuildDirectory func and funcs for
android, aot, asset, ios build products.

Developers may now add a "build-dir" mapping to their
~/.flutter_settings (JSON format) config file. Output directory is
relative to the main flutter application directory.

This change also changes the default build directory for iOS builds to a
subdirectory of the configured build directory, 'build/ios' by default.

* add flutter channel command
fixes https://github.com/flutter/flutter/issues/2513

* fix test

* address comments

* remove unused imports

* fix lints

* enhance flutter upgrade to find project root
fixes https://github.com/flutter/flutter/issues/2990

* address comments

* restore original formatting

* fix lints

has been fully processed before completing the returned future.
This helps prevent tests that rely on stdout from being flaky.

Doesn't do any of the fancy effects. Just lets the user control the
back transition by sliding from the left, like a drawer. Hero
transitions are disabled during the gesture.

BUG=https://github.com/flutter/flutter/issues/4817

This reverts commit 09e68c33.

AOT snapshotter is broken at this engine rev.

https://flutter-dashboard.appspot.com/api/get-log?ownerKey=ahNzfmZsdXR0ZXItZGFzaGJvYXJkclgLEglDaGVja2xpc3QiOGZsdXR0ZXIvZmx1dHRlci8wOWU2OGMzM2NjZGIzNTVmZWRkNzVhODcxNmRlMDU1MWM3NzJmMmRlDAsSBFRhc2sYgICAgICAwAgM

Change the Gallery sample Android package to not conflict with the version published in Play (#5579)

Add update dialog to gallery, open source part of #4626

`Process.start` seems to be escaping as needed.

* test flutter create project dart file is properly formatted

* restore driver-test

* cleanup lint warnings

* address comment

Previously, `flutter build` products were emitted to build/ and only
xcode build products were emitted to $SYMROOT.

If the input test script contains a bad import, sky_shell will fail to
execute main(), in which case a connection to /runner is never
established and the _ServerInfo.socket never completes.

This change works around this by issuing a request on /shutdown when
sky_shell exits.

* don't resolve symlinks as part of which

* update method dartdoc

Changed the ExpandIcon constructor to take a default expansion state.
If the widget gets rebuilt with a different expansion value, the
animation will trigger but the callback will not.

Do not throw when resolving a local engine if the .packages map does not include the flutter package (#5519)

TBR