Remove clips where we can show that they are unnecessary.

Source/core/rendering/RenderBox.h

Index: Source/core/rendering/RenderBox.h
diff --git a/Source/core/rendering/RenderBox.h b/Source/core/rendering/RenderBox.h
index 24562dc32f82d82a9400e8d74a6ec4f6c3fdc9b2..f704c7639bf676e60317f6bbf06b469674fa11a7 100644
--- a/Source/core/rendering/RenderBox.h
+++ b/Source/core/rendering/RenderBox.h
@@ -40,6 +40,9 @@ enum OverlayScrollbarSizeRelevancy { IgnoreOverlayScrollbarSize, IncludeOverlayS
 
 enum ShouldComputePreferred { ComputeActual, ComputePreferred };
 
+enum VisualOverflowClipBehavior { VisualOverflowNotClipped, VisualOverflowClippedByContentsClip };
+enum ContentsClipBehavior { ContentsClipRequired, ContentsClipAutomatic };
+
 class RenderBox : public RenderBoxModelObject {
 public:
     explicit RenderBox(ContainerNode*);
@@ -186,8 +189,10 @@ public:
 
     LayoutRect overflowRectForPaintRejection() const;
 
+    LayoutRect contentsVisualOverflowRect() const { return m_overflow ? m_overflow->contentsVisualOverflowRect() : LayoutRect(); }
+
     void addLayoutOverflow(const LayoutRect&);
-    void addVisualOverflow(const LayoutRect&);
+    void addVisualOverflow(const LayoutRect&, VisualOverflowClipBehavior);

[Julien - ping for review, 2013/08/07 00:17:08]

I would rather see 2 functions instead of adding a mandatory parameter. That
would yield to better code.

[jbroman, 2013/08/08 14:35:39]

Done.

 
     void addVisualEffectOverflow();
     void addOverflowFromChild(RenderBox* child) { addOverflowFromChild(child, child->locationOffset()); }
@@ -470,7 +475,7 @@ public:
     LayoutRect clipRect(const LayoutPoint& location, RenderRegion*);
     virtual bool hasControlClip() const { return false; }
     virtual LayoutRect controlClipRect(const LayoutPoint&) const { return LayoutRect(); }
-    bool pushContentsClip(PaintInfo&, const LayoutPoint& accumulatedOffset);
+    bool pushContentsClip(PaintInfo&, const LayoutPoint& accumulatedOffset, ContentsClipBehavior = ContentsClipRequired);
     void popContentsClip(PaintInfo&, PaintPhase originalPhase, const LayoutPoint& accumulatedOffset);
 
     virtual void paintObject(PaintInfo&, const LayoutPoint&) { ASSERT_NOT_REACHED(); }