Fixes #3741

This patch sizes the menu such that it is always on screen, but doesn't scroll
the menu to ensure that the currently selected item is always visible and on
top of the button. That will need to wait for a later patch.

Also, teach CustomPaint how to repaint animations more efficiently.

Fixes #3720

Prefer implict `equals` matcher in test expectations.

Last literals get their types.

@Hixie: as per our conversation, a little more concise.

This test hangs occationally on the bots and the bots aren't smart enough to
recover, which means the whole project gets blocked.

Filed #3735 about the hang.

Last fixes to get the repo running clean checking for annotations on list and map literals.

Clients of getPosition should just use a one-child custom layout delegate
instead.

Fixes #2484

* First pass at a material-style copy/paste toolbar.

This mimics the toolbar you see when selecting text in an Android
material app. There's still more to do (like integration with the system
clipboard), but this seemed like a good stopping point.

BUG=https://github.com/flutter/flutter/issues/1567

* complain on missing entries in flutter.yaml

* change to a hard failure

More type annotations for literals.

* better parsing of adb devices output

* re-order lines

Fixes #3730

This aligns the analysis options used by 'flutter analyze' with the
options used by Atom.

The `flutter` package gets more types!

Follow-up from: https://github.com/flutter/flutter/pull/3727.

Literals get type annotations.

As per the recent fix to the `always_specify_types` lint (https://github.com/dart-lang/linter/issues/199), literal maps and lists are now expected to be explicitly typed.

Running that lint on the repo identifies quite a few spots to update.  This focuses on `flutter_driver` and `flutter_sprites` (somewhat arbitrarily) but the changes are fairly representative.

Note there are a number of places where I made a quick judgement on how specific to make the types.  Feedback on those is welcome.  (Especially as we move forward with more.)

Turns out we were storing the same object in the base class and the
subclass. For pretty much every AnimatedWidget subclass.

Making progress towards document all public APIs in material.dart. We're still
missing a few odds and ends (as well as missing docs in tabs.dart,
tooltip.dart, and two_level_list.dart).

*  Gallery demo start-time performance test

The same can now be achieved using `flutter run --trace-startup --no-checked`.

* make the usage text more visible

* update the look of the usage text

This patch completes the circuit on this library. The next step is to go
through and add docs to anything we missed.

* ClipPath

* Add a test for ClipOval and ClipPath

We were looking for this service in the wrong service provider.

Fixes #3683

Support for putting assets in android/assets folder (like ios/Resources)

* Track the worst frame in perf tests

* Use backticks in "/// Returns `null` if"

This makes it easier to generate charts that show the engine time and
the framework time separately.

Also, move the default theme transition duration into theme.dart.

* LayoutBuilder Widget