Make Image::image_observer_ WeakPersistent

third_party/WebKit/Source/platform/graphics/Image.h

Index: third_party/WebKit/Source/platform/graphics/Image.h
diff --git a/third_party/WebKit/Source/platform/graphics/Image.h b/third_party/WebKit/Source/platform/graphics/Image.h
index faecfa12c17009613292e2f9ba34fe75877fa299..b3e30393625359732fc2ccdc13bc52726a25714f 100644
--- a/third_party/WebKit/Source/platform/graphics/Image.h
+++ b/third_party/WebKit/Source/platform/graphics/Image.h
@@ -229,9 +229,11 @@ class PLATFORM_EXPORT Image : public ThreadSafeRefCounted<Image> {
   // TODO(Oilpan): consider having Image on the Oilpan heap and
   // turn this into a Member<>.
   //
-  // The observer (an ImageResourceContent) is an untraced member, with the
-  // ImageResourceContent being responsible for clearing itself out.
-  UntracedMember<ImageObserver> image_observer_;
+  // The observer (an ImageResourceContent) is responsible for clearing
+  // itself out when it switches to another Image.
+  // When the ImageResourceContent is garbage collected while Image is still
+  // alive, |image_observer_| is cleared by WeakPersistent mechanism.
+  WeakPersistent<ImageObserver> image_observer_;
   PaintImage::Id stable_image_id_;
 };