Store previous painting clip rects on FragmentData.

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index 7d808bdbffc4a6b75bc6e552cd3ad36ed4eb27a6..ff7ceb45573dd017b2c39ea9eab9085778b4248d 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -1802,10 +1802,12 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
 
    protected:
     friend class PaintPropertyTreeBuilder;
+    friend class PrePaintTreeWalk;
     FRIEND_TEST_ALL_PREFIXES(AnimationCompositorAnimationsTest,
                              canStartAnimationOnCompositorTransformSPv2);
     FRIEND_TEST_ALL_PREFIXES(AnimationCompositorAnimationsTest,
                              canStartAnimationOnCompositorEffectSPv2);
+    FRIEND_TEST_ALL_PREFIXES(PrePaintTreeWalkTest, ClipRects);
 
     // The following non-const functions for ObjectPaintProperties should only
     // be called from PaintPropertyTreeBuilder.
@@ -1825,6 +1827,11 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
           fragment->ClearPaintProperties();
       }
     }
+    FragmentData* FirstFragment() {

[wkorman, 2017/05/01 20:29:24]

nit: add brief documentation, and move impl to .cpp file if we can to avoid
having to rebuild the world if/when we modify this later and to make header file
more readable.

[chrishtr, 2017/05/01 21:43:54]

Done.

+      if (auto* paint_data = layout_object_.GetRarePaintData())
+        return paint_data->Fragment();
+      return nullptr;
+    }
 
     // The following non-const functions for local border box properties should
     // only be called from PaintPropertyTreeBuilder.