Rather than managing all the Material Design icons manually, we now
manage them using an icon font. The icon font contains glyphs for each
icon in an efficient vector format.
This patch updates the FLX tooling to include the MaterialIcons font and
updates the Icon widget to use the font instead of asset images.
Fixes#2313Fixes#2218Fixes#2009Fixes#994
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.
