Fix a large number of Drawer bugs

This patch restructures how we handle drawer. The drawer is now a child of the
Scaffold, which wraps the Drawer in a DrawerController. The DrawerController
manages the interaction with the navigator as well as the edge swiping. The
DrawerController's state machine is driven almost entirely off its Performance,
which it now owns completely.

Fixes #90
Fixes #187
Fixes #192
Fixes #194
Fixes #604

buildForwardTransition()

For those times when you want to do something as you move away from a
route into the next one, as well as when you move into it from the
previous one.

Rename some of the functions from the scheduler.

The names are probably less familiar, but more consistent:
- FrameCallback: a callback that is relative to the frame and wants the
  frame offset (a duration) as argument.
- addXFrameCallback: adds the given callback to the internal lists/maps.
- scheduleXFrameCallback (currently only X = ""): add the callback, but
  also trigger a new frame.
- handleX: the method that is invoked when the event-loop or the frame
  calls into the scheduler.
- ensureXYZ: ensure that the callback happens.
  Unfortunately there is the ambiguity between a "callback": it can be a
  closure, or the action of doing a callback, so we end up with:
  ensureBeginFrameCallback, and ensureEventLoopCallback, where
  "callback" means the action of being called back.

Add missing import to flutter_sprites

Add liftToOverlay to Mimicable

This patch integrates Mimicable with Overlay such that you can tell a Mimicable
to lift up into the overlay and animate towards another widget identified by a
global key.

Fix a typo in _CircularProgressIndicatorPainter

Make trace --stop fail if the adb pull fails.

@chinmaygarde

Rename _updateScrollBehaviour to _updateScrollBehavior

Fix crash when going back in stocks app.

Fixes #675

Heroes with the same tag have to have keys that are unique across the
entire subtree. Since we can now show both stock lists, this means we
have to include the tab in the heroes' keys.

Fixes #668.

Remove animation scheduler.

Merge the two schedulers.

Initialize the track color fields in _RenderSwitch

Add output to "flutter apk" indicating where the APK file was written

Generate an Android manifest in "flutter init"

Remove the assert when opening popup menus.

Some paint bounds are in fact empty, e.g. at the start of a growing
animation if there's also a fade, the initial 0x0 box will also be
opacity:0, and might get a dedicated layer and PaintingContext.

Model ink splashes more physically

Update package:test to the latest version

Makes it easier to hit IconButton

The right fix here is to use a radial reaction, but for now we can just make
the gesture detector including the padding acround the icon in its hit test
region.

Fixes #575

Fix Input padding to match the material spec

Also, handle the case of "dense" input widgets that have less margin.

Fixes #626

Add input#hideText

This feature can be used to implement password fields, where the user doesn't
want the text displayed on screen. Currently all the characters are hidden.
Eventualy we'll want to show the most recent character for some timeout.

Fixes #636