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

* fix analysis errors

* review comments; fix test

* re-add an export for debugPrint

Add note about explicit `pub get` needed.

Fixes https://github.com/flutter/flutter/issues/3493

 - rebuild stateless widgets that have dependencies when their ancestors change but they don't

Fixes https://github.com/flutter/flutter/issues/3120

 - rebuild widgets that tried to inherit from a widget that didn't exist, when the widget is added

This adds a pointer and a bool to Element, which isn't great. It also adds a more or less complete tree walk when you add a new Inherited widget at the top of your tree, which isn't cheap.

@devoncarew @jason-simmons

If there's a max height or width, we should factor that into the intrinsic
sizing for the other dimension.

We need to import these enums in order for the dartdoc to linkify correctly.

Fixes #3668

Check the adb install output for errors and stop "flutter run" if package installation fails (#3672)

Also update the engine to a build where these tools have been uplaoded

Fixes #3624

* Revert "Revert "Mega gallery (#3647)" (#3659)"

This reverts commit ea62d31f.

* fix the dev/dartdoc.dart script

This reverts commit 9497fb56.

This patch broke the dartdoc step on the bots.

Pick up a bug fix to the `usage` package.

* working on a large benchmark app

* build a 100k saple app

* print sizes of other libs; scale to 60k lines

* test the generated app on travis

Instead of incorporating the margin into the button, introduce a ButtonBar
widget that supplies the proper spacing between the buttons. Also, make these
buttons more configurable via ButtonTheme so that dialogs can change the
minWidth and padding of the buttons as required by the spec.

Fixes #1843
Fixes #3184