Includes:
flutter/engine#4427
flutter/engine#4428

Includes:
flutter/engine#4422 (Dart SDK roll)

* Remove unnecessary error message

* Add AUTHOR

Updates scaffold to expose bottom padding to the associated
BottonNavigationBar (if present). BottomNavigationBar is now responsible
for adjusting itself to account for bottom padding.

This change is necessary to support the updated BottomNavigationBar
layout for the iPhone X.

* Remove MediaQuery padding for various PopupRoutes that don't extend to the edge of the screen

* bottom sheet doesn't actually need handling. Scaffold does it already. Add test for others.

Now that keyboard height is modelled as a (bottom) view inset, migrate
scaffold bottom resizing to use view insets instead of bottom padding,
which, after an engine roll, will only be used for safe areas.

Until the aforementioned engine roll, the keyboard height is still
included in both bottom padding and view insets. As such
resizeToAvoidBottomPadding still drives bottom padding removal until
that roll lands.

Renames _ScaffoldLayout.bottomPadding to bottomViewInset

Also adds a TODO that should have landed with flutter/flutter#13423.

This patch contains no framework changes.

This change adjusts a test bottom navigation bar height to be greater
than the media bottom padding.

This change is pre-factoring to clarify diffs in an upcoming change that
will expose bottom padding to the bottom navigation bar in order to
allow it to visually adapt its appearance in the presence of bottom
padding such as thatexposed for the iPhone X home screen indicator.
Since the bottom padding was previously greater than the height of the
bottom navigation bar, the height of insideBottomNavigation bar was
driven to 0 when padding is exposed.

This allows the scheduler library to depend on the services library
and the painting library to depend on the scheduler library without
the services library having to depend on the scheduler library.

While I was at it I also cleaned up some of the binding logic: the
licenses logic can now be overridden (and the test library does so),
and the image cache can now be overridden as well.

This reverts commit 9315a79b.

There is an unfortunate interaction with verifyThenRunCommand

Scaffold bottom padding now applies the maximum of window
viewInsets.bottom (typically used for iOS safe areas) and padding.bottom
(typically used for keyboard height).

Make regular Alignment values look more like enumProperties while
leaving more complex AlignmentDirectional values unchanged.

* route device issue diagnostics to flutter doctor

* review comments

* review comments

Add support for configuring the base storage URL for Flutter's
artifacts. If FLUTTER_STORAGE_BASE_URL is set, use it instead of
storage.googleapis.com.

The pub server can be overridden by setting PUB_HOSTED_URL.

This reverts commit f40a9398.

* Emulate text entry in FlutterDriver

* document enterText behavior

* remove the unnecessary composint TextRange

Rolls:
flutter/engine#4411
flutter/engine#4416
flutter/engine#4420
flutter/engine#4421
flutter/engine#4423

* Add a cylindrical projection helper matrix

* specify tangential

* more doc clarifications

* reshuffle arguments

* more code comments

* add some sanity tests

* review

* review 2

* added one more caveat for consideration in docs

This contains a breaking API change to `SelectionChangedHandler`.

This is part of making text input accessible on Andriod (https://github.com/flutter/flutter/issues/12785).

This picks up a single commit: flutter/engine#4418, which fixes #12585.

Adds a class `PubContext` with a fixed set of allowed values
Make it clear these values should not be changed casually

Fixed one inconsistency already: update_packages vs update_pkgs
Provide more information for verify calls
Eliminate `ctx_` prefix.

This adjusts the CupertinoTabBar height in the presence of bottom
padding. On the iPhone X, this will increase the height to account for
the home indicator widget.

The purpose of this PR is to make it so that when the user runs 'flutter', if they have a .pub-cache directory in their flutter root, we use that instead of the default location for the pub cache. Otherwise, it should act as before.

The eventual goal is to support a pre-populated flutter .zip/.tar.gz file that has everything the developer needs in one bundle. In order for that to actually work, we need to have the pub cache be self-contained, and not in the user's home dir.

Another advantage of this is that if you have multiple flutter repos that you're switching between, then the versions in the pub cache will remain static when you switch between them.

This is an attempt to re-land: #13248. Includes a fix for the test that makes it work on bots in the presence of PUB_CACHE being set, and no other changes.