Add ShaderErrorHandler to GrContextOptions

Allows clients to customize behavior when shaders fail to compile.
Added nicer shader error handling to viewer.

Change-Id: If82b48e40d64fd786f37e88c564fd623b53c7f9d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/211361
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
15 files changed