Invalidate GrTexture mipmap on content change notification

include/core/SkPixelRef.h

Index: include/core/SkPixelRef.h
diff --git a/include/core/SkPixelRef.h b/include/core/SkPixelRef.h
index 3898269ef458e16440ae09006ceb34fbe199f16f..c02664df7d51f81f20a50b4c62ae01032230f819 100644
--- a/include/core/SkPixelRef.h
+++ b/include/core/SkPixelRef.h
@@ -313,6 +313,9 @@ protected:
     // default impl returns NULL.
     virtual SkData* onRefEncodedData();
 
+    // default impl does nothing.
+    virtual void onNotifyPixelsChanged();
+
     // default impl returns false.
     virtual bool onGetYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3],
                                  SkYUVColorSpace* colorSpace);