Add Android framework only util to get the SkSurface from SkCanvas

This API enables the framework to implement unclipped saveLayer
calls in a more efficient manner, by requiring fewer render target
switches on the GPU.

Bug: b/119222339
Change-Id: I7276675a4c1389f8493d2583ff7d6533b57a7b3b
Reviewed-on: https://skia-review.googlesource.com/c/173102
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>
2 files changed