We now use the `@required` annotation to encourage developers to
explicitly set onPressed and onChanged callbacks to null when that would
disable the widget.

Fixes #287

This file is now app.dylib.

See https://github.com/flutter/flutter/issues/4438

Bump Dart SDK to patched stable.

Cleans up a few style nits in hello_services and adds support for automatic
JSON encoding and decoding to the HostMessages interface.

- Fix the background color and AppBar transparency on the Recipe page.
- Use a Hero animation for the recipe card.
- Draw the background image under the status bar on the recipe page.
- Added instructional text on favorites page when there are no favorites.

BUG=https://github.com/flutter/flutter/issues/4403
BUG=https://github.com/flutter/flutter/issues/4405
BUG=https://github.com/flutter/flutter/issues/4436
BUG=https://github.com/flutter/flutter/issues/4399

`1.17.1` fixes:
* crash in async functions
* GC bug in weak properties

Relevant patches here:
* https://github.com/dart-lang/sdk/issues/26680
* https://github.com/dart-lang/sdk/issues/26681

This repo contains the final licensed images.

Fixes #4427

If you tap outside the drop down menu while its animating in, we should
animate it away smoothly. Previously, we jumped to the reverseCurve,
which made the menu disappear immediately. Now we hold the animations as
state, which means we keep their _curveDirection property and don't
switch curves unless the animation actually finishes.

Also, fix a subtle bug in CurvedAnimation whereby we'd never set the
_curveDirection if we didn't see a status change in the parent
animation. Now we initialize _curveDirection based on the current value
of the parent's status.

Fixes #4379

Fixes #4425

Instead of using getTotalMatrix and setMatrix, we can just use
save/restore, which is more idiomatic.

The getTotalMatrix/setMatrix pattern was introduced to improve
performance, but the original code was calling getTotalMatrix/setMatrix
at every node in the sprite tree, which is much slower than the normal
save/transform/restore pattern.

Related to #4254

Fixes #4059

Fixes #4428

Also renames ButtonTheme.footer to ButtonTheme.bar.

We're explicitly saying that making these icons do anything useful is
out of scope, so the best we'll do here is show a snackbar.

* Add a 'Return to Gallery' drawer option to Pesto.

BUG=https://github.com/flutter/flutter/issues/4402

* oops

* support --route in flutter run --resident

* also for the daemon app.start command

Also update the assets version to pull in better quality logo images.

BUG=https://github.com/flutter/flutter/issues/4407

* Add a map of relative to absolute paths for assets located outside the app's
  source directory
* If a "packages" directory exists, obtain assets from there instead of
  using the packages/ prefix to indicate package map lookup

Bump to stable 1.17.0 Dart SDK.

Update the analytics code.

Also, make sure that the parent is notified when they change.

Fixes #2298

It's TODONE

We can viewport the content using a ScrollableGrid. Also, we can use the
padding mechanisms of the grid to avoid extra padding widgets.

1. Use the primary color brightness to determine the color of the status bar.
    The status bar overlaps the toolbar, which has the primary color.
 2. Use Roboto for text.

We have these details objects for the same reason we now have drag details
objects: future extensibility.

Fixes #4421

Also:
* Make PaginatedDataTable able to scroll itself horizontally.
* Make drop down buttons support having an explicit text style and icon
  size given.
* Fix a bug with drop-down buttons asserting when opened partly
  off-screen.
* Make sure to pop the drop-down button's route if the drop-down button
  is discarded while the route is up.
* Remove extraneous padding on drop-down buttons. (Couldn't figure out
  why it was there, and it breaks alignment when a drop-down is mixed
  with other text.)
* Some docs improvements.
* Add Route.isActive
* Add a setState() method to ModalRoutes.

I was also going to implement sorting and emptying the cart but the
current data model doesn't make that easy, so I gave up on that. That's
why the TODOs are moved around though.