cc: Devirtualize DisplayItem::ExternalMemoryUsage().

cc/playback/float_clip_display_item.h

Index: cc/playback/float_clip_display_item.h
diff --git a/cc/playback/float_clip_display_item.h b/cc/playback/float_clip_display_item.h
index 744aac15f54d156088fc5bdfb04a99c5b55d632c..7f39ad6315680cac5230a38f9a9ef668015c0bf6 100644
--- a/cc/playback/float_clip_display_item.h
+++ b/cc/playback/float_clip_display_item.h
@@ -30,8 +30,8 @@ class CC_EXPORT FloatClipDisplayItem : public DisplayItem {
               SkPicture::AbortCallback* callback) const override;
   void AsValueInto(const gfx::Rect& visual_rect,
                    base::trace_event::TracedValue* array) const override;
-  size_t ExternalMemoryUsage() const override;
 
+  size_t ExternalMemoryUsage() const { return 0; }
   int ApproximateOpCount() const { return 1; }
 
  private:
@@ -55,7 +55,6 @@ class CC_EXPORT EndFloatClipDisplayItem : public DisplayItem {
               SkPicture::AbortCallback* callback) const override;
   void AsValueInto(const gfx::Rect& visual_rect,
                    base::trace_event::TracedValue* array) const override;
-  size_t ExternalMemoryUsage() const override;
 
   int ApproximateOpCount() const { return 0; }
 };