This adds an API for defining the semantic node traversal order.

It adds a sortOrder argument to the Semantics widget, which is a class that can define a list of sort keys to sort on. The keys are sorted globally so that an order that doesn't have to do with the current widget hierarchy may be defined.

It also adds a shortcut sortKey argument to the Semantics widget that simply sets the sortOrder to just contain that key.

The platform side (flutter/engine#4540) gets an additional member in the SemanticsData object that is an integer describing where in the overall order each semantics node belongs. There is an associated engine-side change that takes this integer and uses it to order widgets for the platform's accessibility services.

* Keep the intermediate APK signed the same way before going to the play store

* Don't run on PRs

Discovered during an a11y review of the gallery.

Previously, the iOS ApplicationPackage subclasses did not mark the
bundleID constructor parameter as @required. This is passed up to the
ApplicationPackage constructor as the id parameter which is already
marked @required and is asserted to be non-null.

When diagnosing a failed Xcode build, if neither the development team
(for automatic provisioning) nor the provisioning profile (for manual
provisioning) is set, display the appropriate error message. Previously,
this method would not output the appropriate error message if a
only a development team was set.

- Add override of border color of CupertinoNavigationBar
- Add background color to CupertinoPageScaffold

* Fix scrolling of multiple SliverLists and SliverGrids

* Update sliver_fixed_extent_list.dart

* Update sliver_grid.dart

* iOS works

* Works on Android

* Take in commit number in iOS also. Get rid of image upload for Android. It's just a waste of bandwidth

* Tweak to fix on Travis

* Widget Inspector support for tracking Widget creation locations.

* Add arguments to dartdoc.dart for Dartdoc's grinder and travis

* Fix bug in filter

Fixes https://github.com/flutter/flutter/issues/14393

For example, so that the gallery can override the media query globally.

* work around const lints

* update nonconst doc

* bump the dart sdk version to 2.0.0-dev.17.0

* 2.0.0-dev.20.0

* 2.0.0-dev.19.0

* Flatten change out from lots of merges and temporary hacks for #7224

* Expand fakes to cover cases where doctor passes

* -v != --verbose

* Cosmetic touchups

* delint

* Clean up summary line, add a switch for review comments

* Review comments

* nit

* review comment

* review comments

* Populate AnsiTerminal in context for daemon launches

* Strip out AnsiTerminal additions to context since they are no longer needed

Using a void list literal in this case is valid and correct, and will be
required for dart 2.

Note: void can be inferred here, but followed the lints to write it
explicitly even though that's arguably a bit weird in this case and less
backwards compatible.

Note: also fixes a bug wherein bottom media padding was applied even in the
presence of persistent footer buttons.

The material spec states that the keyboard should be positioned on top
of any bottom navigation bar or persistent footer buttons widget(s).

We no longer inset the bottom of bottom navigation bars / persistent
footer buttons by the bottom viewInset.

Body content bottom (and the bottom of bottom sheets) is now determined
by the greater of:
  1. bottom view inset (the keyboard height)
  2. bottom elements (nav bar, footer buttons)
relative to the window max-Y.

Add meta tag @optionalTypeArgs to the mixin classes where we don't expect a generic type to be specified at the points where the mixin is applied. This suppresses the analyzer warnings.