Enable the tessellation atlas for general path rendering

This is a drastic change to how non-MSAA paths are rendered in Chrome.
After this CL, and as long as multisample support is enabled, non-convex
paths with 256^2 pixels or fewer will be rendered by tessellation in a
2048x2048 multisampled alpha8 atlas. This will give tremendous
improvements in path rendering times and overall CPU usge. This change
will also cause Skia to quit caching path bitmaps in many cases, so we
can expect to see some memory savings. Dropping the path cache is not
expected to impact performance much because the tiles themselves are
their own bitmap cache.

Bug: chromium:928984
Bug: skia:12258
Change-Id: I1a4e2dba65d2db4a74f766aa944e4a64782df271
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3062518


Auto-Submit: Chris Dalton <csmartdalton@chromium.org>
Commit-Queue: Chris Dalton <csmartdalton@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Justin Novosad <junov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#907388}