This is a reland of #5638. We removed the restoreToCount, made doAntiAlias named, and updated the comments.

This reverts commit a2bf8059.

Reason for revert: need to fix several things including the framework test in order to unblock the engine roll.

TBR: @matthew-carroll 

This would enable us to solve https://github.com/flutter/flutter/issues/18057

This reverts commit d8740c70.

* format

* license script adaptions

* updated licenses

* review comments

Without this, the cull rect calculated by an SkPicture may be truncated
to integer pixel coordinates.  The raster cache relies on a precise cull
rect in logical coordinates.

See https://bugs.chromium.org/p/skia/issues/detail?id=6954

This attempts to make the Canvas API and some related features more
likely to throw a Dart exception than crash when exposed to bad input.

Depends on rolling tonic to
https://fuchsia-review.googlesource.com/c/35742/ which this patch does
not yet do, but I wanted to put it up for review to see if it was even
a reasonable approach.

This will ensure that the engine is not broken by a future
skia roll.

Fixes https://github.com/flutter/flutter/issues/8809

The Skia team says these APIs are outdated and should be removed. They
do not appear to have any clients.

Fixes https://github.com/flutter/flutter/issues/7202
Fixes https://github.com/flutter/flutter/issues/7204

The Skia team tells us that these go faster.

* Added drawArc to Canvas.

Added a way to call SkCanvas::drawArc from Dart. This method is
optimized for the arc case and should be faster that drawing paths.

* Removed implementation details from docs.

* Added more details to the docs.

This removes most (all?) of our dependency on base::RefCountedThreadSafe.

Also, switch over to //lib/tonic's typed data classes.

This patch moves the remainder of painting and compositing into their
new home (and updates their style to match Google C++ Style).