only notify bitmaps that have been added to the cache

src/gpu/SkGrPixelRef.cpp

Index: src/gpu/SkGrPixelRef.cpp
diff --git a/src/gpu/SkGrPixelRef.cpp b/src/gpu/SkGrPixelRef.cpp
index b0e89092cb195e3837ef24ffca2a804f3ced28f2..01444af705d8d0ec69023ec05a02e14623e914a0 100644
--- a/src/gpu/SkGrPixelRef.cpp
+++ b/src/gpu/SkGrPixelRef.cpp
@@ -189,7 +189,7 @@ bool SkGrPixelRef::onReadPixels(SkBitmap* dst, const SkIRect* subset) {
         // If we are here, pixels were read correctly from the surface.
         cachedBitmap.setImmutable();
         //Add to the cache
-        SkBitmapCache::Add(this->getGenerationID(), bounds, cachedBitmap);
+        SkBitmapCache::Add(this, bounds, cachedBitmap);
 
         dst->swap(cachedBitmap);
     }