Fix drawBitmapRect in the threaded backend

Previously, the threaded backend failed to drawBitmapRect (see,
e.g., GM_bitmaprect_s) because it did not intercept the call to
SkDraw::drawBitmap.

Bug: skia:
Change-Id: I7eeaae98e63d726b2b566c4d15f7ea939f59360e
Reviewed-on: https://skia-review.googlesource.com/115983
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>
4 files changed