SkPaintFilterCanvas should inherit the target canvas state

Currently, SkPaintFilterCanvas does not provide any help in cloning
target canvas state.  While that could be handled in subclasses, it is
easy to miss (see linked bug).

This CL adds a new constructor variant which ensures that the initial
matrix and clip bounds are inherited from the target canvas.

BUG=516790
R=reed@google.com,robertphillips@google.com

Review URL: https://codereview.chromium.org/1294013002
3 files changed