And fix the zillion issues that uncovered.

This reverts commit f41b3411, reversing
changes made to e33d8d96.

This was a bad check-in due to my mangling uploading a new version of the branch from a different machine.

This reverts https://github.com/flutter/flutter/pull/2639 and will be replaced by https://github.com/flutter/flutter/pull/2640

And fix the zillion issues that uncovered.

Well, all the easy ones, anyway.

For some reason `// ignore:` isn't working for me so I've disabled
lints that need that. Also disabled those that require a ton of work
(which I'm doing, but not in this PR, to keep it reviewable).

This adds:
- avoid_init_to_null
- library_names
- package_api_docs
- package_names
- package_prefixed_library_names
- prefer_is_not_empty
- sort_constructors_first
- sort_unnamed_constructors_first
- unnecessary_getters_setters

Drawer doesn't need a SizeObserver, since it only looks at the size
in event handlers. It can just go and probe the tree to read the size.

Also, change from using _kEdgeDragWidth to using _kWidth when figuring
out how much of the drawer to show when dragging it from the edge, since
that is more likely to match the drawer's width.

Each layer is supposed to reexport the parts of the previous layer
that are part of its API.

- In painting.dart, export from dart:ui all the Canvas-related APIs
  that make sense to be used at higher levels, e.g. PaintingStyle.

- Delete painting/shadows.dart. It was dead code.

- In rendering/object.dart, export all of painting.dart.

- In widgets/basic.dart, export all of painting.dart and
  animation.dart. Some classes in animation/ are renamed to make this
  less disruptive and confusing to the namespace.

- Split out Stocks back into an import model rather than a part model,
  so that it's easier to manage its dependencies on a per-file basis.

- Move Ticker to scheduler library.

- Remove as many redundant imports as possible now.

- Some minor nit picking cleanup in various files.

- make them all have the same style
- make them all include the stack trace last
- make them all stop printing if their callback is set (if
  appropriate, they don't yet all have callbacks)

This is a workaround for:
   https://github.com/dart-lang/sdk/issues/25246

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.

The current implementation is still pretty rudimentary.