Clean up some legacy shader context code

The base class returns nullptr, so no need for various derived classes
to do the same thing.

A bigger simplification is that SkPictureShader doesn't need to create a
custom context class that just acts as a pass-through to an image shader
context - just return the image shader context directly.

Change-Id: I11314a399b01f078e91afb723ba225d92b34f22c
Auto-Submit: Brian Osman <>
Commit-Queue: Brian Osman <>
Reviewed-by: Kevin Lubick <>
Commit-Queue: Kevin Lubick <>
5 files changed