Fix Android overdraw detection

Now that SkNWayCanvas inherits from SkNoDrawCanvas, we need to
override onDrawDrawable().

BUG=skia:

Change-Id: Id8cf62f5675199202580d3ee94c71a0ae231c81e
Reviewed-on: https://skia-review.googlesource.com/5865
Commit-Queue: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
2 files changed