In a scaffold, snackbars are positioned above the BottomNavigationBar
and/or PersistentBottomButtons, if present. In such cases, they should
not apply bottom media padding to their widget sub-tree.

With a little refactor and unification of how availability of copy/cut/paste is determined across platforms.

Minor remaining issue: https://github.com/flutter/flutter/issues/14331.

Fixes https://github.com/flutter/flutter/issues/13501.

* first round fastlane working on Android

* clean up and start ios

* Partial iOS

* Got a fastfile that works on iOS

* Finalize Android push instructions

* Finalize instructions for iOS

* Extra cleanup and optipng

* Disable readme autogen and add a default readme

* [kernel/flutter] Improve speed of first hot reload

* [kernel/flutter] Improve speed of first hot reload

* Revert "[kernel/flutter] Improve speed of first hot reload"

This reverts commit f3dc133878ec7405a8efb5715f1cfe720f4ea05f.

* Revert "[kernel/flutter] Improve speed of first hot reload"

This reverts commit f7bcb082b01cf9cf48f02c6aad9e5c79705def8f.

* Revert "Revert "[kernel/flutter] Improve speed of first hot reload""

This reverts commit 73c7a1a8e85a4c0397984d8b65a98b2f71bf84f3.

* [kernel/flutter] Improve speed of first hot reload

Do so by not evicting unnecessary paths (while still evicting paths
that was changed between the generation of the package file and the
initial upload).

* Fix grammar in method name

* Fix bad merge

* Add method to super class

This triggered an analysis failure only on the devicelab.

For backward compatibility we keep supporting specifying the shape as a
combination of MaterialType and borderRadius, and we just use that as a
default when shapeBorder is null.

To cleanup the implementation if shapeBorder was not specified we just
translate the specified shape to a shapeBorder internally.
I benchmarked paint, layout and hit testing, with the specialized shape
clippers vs. the equivalent path clippers and did not see any
significant performance difference.

For testing, I extended the clippers/physicalShape matchers to match either the
specialized shape or the equivalent shape.

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