Replace CanvasResource_Skia with CanvasResource_Bitmap

This change refactors the existing CanvasResource_Skia to make it
store a StaticBitmapImage instead of an SkImage intenally. This
simplifies the gpu mailbox management code by re-using the
functionality provided by StaticBitmapImage. It also bring the code
closer to unifying OffscreenCanvasResourceProvider with
CanvasResourceProvider

BUG=788439,776801
TBR=bajones@chromium.org

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Ia57a68e1a61763daa158403e258b89b56a82a6f7
Reviewed-on: https://chromium-review.googlesource.com/820251
Commit-Queue: Justin Novosad <junov@chromium.org>
Reviewed-by: Olivia Lai <xlai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524204}
20 files changed