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..c0019c14d21a6768bbd81f4ac18436d95f837221 100644
--- a/Source/core/rendering/RenderBox.h
+++ b/Source/core/rendering/RenderBox.h
@@ -40,6 +40,8 @@ enum OverlayScrollbarSizeRelevancy { IgnoreOverlayScrollbarSize, IncludeOverlayS
 
 enum ShouldComputePreferred { ComputeActual, ComputePreferred };
 
+enum ContentsClipBehavior { ContentsClipRequired, ContentsClipAutomatic };

[Julien - ping for review, 2013/08/08 21:36:50]

Those names could use some improvement: "automatic" is a very undefined word.

Here are some better names:
* ForceContentsClip, SkipContentClipIfPossible
* ContentsClipForced, ContentClipMayBeIgnored

[jbroman, 2013/08/09 15:34:35]

Took your first suggestion.

+
 class RenderBox : public RenderBoxModelObject {
 public:
     explicit RenderBox(ContainerNode*);
@@ -186,9 +188,14 @@ public:
 
     LayoutRect overflowRectForPaintRejection() const;
 
+    LayoutRect contentsVisualOverflowRect() const { return m_overflow ? m_overflow->contentsVisualOverflowRect() : LayoutRect(); }
+
     void addLayoutOverflow(const LayoutRect&);
     void addVisualOverflow(const LayoutRect&);
 
+    // Clipped by the contents clip, if one exists.
+    void addContentsVisualOverflow(const LayoutRect&);
+
     void addVisualEffectOverflow();
     void addOverflowFromChild(RenderBox* child) { addOverflowFromChild(child, child->locationOffset()); }
     void addOverflowFromChild(RenderBox* child, const LayoutSize& delta);
@@ -470,7 +477,7 @@ 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);

[Julien - ping for review, 2013/08/08 21:36:50]

There are 3 callers, let's avoid the default parameter.

[jbroman, 2013/08/09 15:34:35]

Done.

     void popContentsClip(PaintInfo&, PaintPhase originalPhase, const LayoutPoint& accumulatedOffset);
 
     virtual void paintObject(PaintInfo&, const LayoutPoint&) { ASSERT_NOT_REACHED(); }