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If rendering code that is shared with GrContext changes any GL state,
then skia caches need to be notified.  This adds InvalidateGrContext()
method that will call private pure virtual method.  InvalidateGrContext
default argument will clear all state in GrContext.

Updated classes that derive from ContextProvider.

R=piman@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1131723002

Cr-Commit-Position: refs/heads/master@{#329255}