This updates the CupertinoAlertDialog to respect text scale factor more properly. Before this, it would scale, but would clip the action buttons at large scales, and would draw in the safe area. It also didn't match the iOS alert because the content didn't scroll. Now it does those properly.

I didn't address the fact that buttons should lay out properly (Issue #14345), but that's probably pretty low priority.

Fixes #12484

Includes:
* Only implement application:performActionForShortcutItem:completionHandler on iOS 9.0+ (flutter/engine#4600)
* [fuchsia] Remove MessageLoopHandler dependency (flutter/engine#4618)
* Use @available checks for iOS 11 features (#4619)

* Try to make transitioning channels actually work.

* Update upgrade.dart

Includes:
* Roll Dart SDK (flutter/engine#4613)

This script will update release metadata in the cloud, and copy the already-built package to the right location and name on cloud storage.

The release metadata will be located in gs://flutter_infra/releases/releases.json, and the published packages will end up in gs://flutter_infra/releases/<channel>/<platform>/flutter_<platform>_<version><archive suffix>, where <channel>, <platform>, <version>, and <archive suffix> are determined by the script.

At the moment, it only supports dev rolls, but (once we know how those will work) should easily support beta rolls as well.

* Add a callback that fires when a Draggable leaves a DragTarget.  This enables the DragTarget to manage its state from entry to exit.

* It helps to have a null check here

* Add test for onLeave callback and add verbiage to onWillAccept explaining the callback lifecycle of a DragTarget.

* adds crossAxisEndOffset and rollbackDuration properties to dismissible widget

* re-added removed license comment

* corrected license comments

* Adds test for rollbackDuration and crossAxisEndOffset

* added tests and comments

* modified tests for dismissible widgets

Includes:
* Remove unnecessary trim (#4616)

It adds lines like `SHARD=analyze` to each shard, and a message like `Contents of packages/flutter_localizations/lib/src/l10n/localizations.dart matches output of gen_localizations.dart script.`  to the analysis shard.

Includes:
* Extract common iOS asset path lookup code: #4594
* Introduce VulkanProvider fb9782a5294e700e45e372da0cd25165697b2e45
* Transition render target images before submit 0de8218778f1bb5d913db8b8a67789a44f8bb28f
* Update buildtools to Fuchsia HEAD #4599

* Add onCancelled callback to PopupMenu

* Fix spelling, don't call onCanceled if disposed, improve documentation.

* Make the current command injected into the AppContext, allowing
  other classes to inject the current command.
* Introduce `AssetBundleFactory`, an injected factory class for
  spawning instances of `AssetBundle`. This allows other run contexts
  to use custom asset bundling logic.
* Clean up RunCommand by removing a 'packages' argument that duplicated
  a global argument by the same name (and for the same purpose).
  Duplicate arguments are confusing and error-prone.

This was overlooked in 5e18c076

* Fix shadows in NestedScrollView

The previous logic (and especially the previous test) wasn't quite right.

* Update nested_scroll_view.dart

This widget evolved over time by multiple people, I'm just trying to explain
in a more direct way what the widget is currently doing.

When running with --preview-dart-2, host variant of the engine is
required. Simulator builds, like device builds, should resolve
host_RUNTIMEVARIANT_OPTVARIANT, not host_RUNTIMEVARIANT_sim_OPTVARIANT.

Fixes https://github.com/flutter/flutter/issues/14232

(I haven't tested this with older versions of git, I'm just going on
what @jason-simmons wrote in the bug.)

* Point to master API docs

I _think_ this is the right place, since people contributing and working on master might care about where the API docs are for master branch.

* Update CONTRIBUTING.md

update from review comment

* Roll engine to 6921873c71e700235c0f68f0359be2332f93c8bc

Also some trivial improvements to style.

Roll engine to 7c34dfafc9acece1a9438f206bfbb0a9bedba3bf

* 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.

The code was attempting to delete temporaryDirectory while it should have been deleting tempBundleDirectory

* controller, position and test

* Make controllers swappable

* WIP

* Create a ListWheelScrollPhysics

* Created picker and gallery demo and testing now

* Works. Ready to document and test.

* Document and add tests. Make the scroll controller more generic.

* minor cleanup

* review

* review

* fix tests

* stop using TransformLayers for now

This reduces the jank of bringing up the license screen further.
The remaining lost frame or two are caused by Dart itself, see:

   https://github.com/dart-lang/sdk/issues/31954
   https://github.com/dart-lang/sdk/issues/31959
   https://github.com/dart-lang/sdk/issues/31960

Fixes https://github.com/flutter/flutter/issues/5187