Revert "Reworks the clipping logic" and follow-up.

Source/core/paint/DeprecatedPaintLayerClipper.h

Index: Source/core/paint/DeprecatedPaintLayerClipper.h
diff --git a/Source/core/paint/DeprecatedPaintLayerClipper.h b/Source/core/paint/DeprecatedPaintLayerClipper.h
index a0303716c08c6eb070bd53d13e5d246f8d256bca..4f64cd0ebe2321300bb611e18aeef89f3512f637 100644
--- a/Source/core/paint/DeprecatedPaintLayerClipper.h
+++ b/Source/core/paint/DeprecatedPaintLayerClipper.h
@@ -45,7 +45,6 @@
 #ifndef DeprecatedPaintLayerClipper_h
 #define DeprecatedPaintLayerClipper_h
 
-#include "core/layout/ClipRects.h"
 #include "core/layout/ClipRectsCache.h"
 #include "core/layout/LayoutBox.h"
 #include "wtf/Allocator.h"
@@ -54,25 +53,6 @@ namespace blink {
 
 class DeprecatedPaintLayer;
 
-// This is the state information passed down
-// on the stack for calculating clip rects.
-struct ClipRectComputationState {
-    STACK_ALLOCATED();
-    ClipRectComputationState()
-    {
-        currentClipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
-        stackingContextClipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
-    }
-    // Depending on the value of context.isComputingPaintingRect() can have different meanings
-    // In painting, this ClipRects is used for statically positioned elements,
-    // outside painting, it is the only ClipRects, and is used for all elements.
-    ClipRects currentClipRects;
-    // During painting this ClipRects is used for positioned elements. It can have
-    // a rootLayer further up the tree than currentClipRects because its root must be
-    // beyond the enclosing stacking context. See resetPaintRects.
-    ClipRects stackingContextClipRects;
-};
-
 enum ShouldRespectOverflowClip {
     IgnoreOverflowClip,
     RespectOverflowClip
@@ -149,25 +129,33 @@ public:
     // Pass offsetFromRoot if known.
     void calculateRects(const ClipRectsContext&, const LayoutRect& paintDirtyRect, LayoutRect& layerBounds,
         ClipRect& backgroundRect, ClipRect& foregroundRect, ClipRect& outlineRect, const LayoutPoint* offsetFromRoot = 0) const;
-    void calculateClipRects(const ClipRectsContext&, ClipRectComputationState&) const;
-
-    DeprecatedPaintLayer* clippingRootForPainting() const;
+private:
+    void calculateClipRects(const ClipRectsContext&, ClipRects&) const;
+    ClipRects* clipRectsIfCached(const ClipRectsContext&) const;
+    ClipRects* storeClipRectsInCache(const ClipRectsContext&, ClipRects* parentClipRects, const ClipRects&) const;
 
-    void precalculateAbsoluteClipRects();
+    // cachedClipRects looks buggy: It doesn't check whether context.rootLayer and entry.root match.
+    // FIXME: Move callers to clipRectsIfCached, which does the proper checks.
+    ClipRects* cachedClipRects(const ClipRectsContext& context) const
+    {
+        return m_cache ? m_cache->get(context.cacheSlot()).clipRects.get() : 0;
+    }
+    void getOrCalculateClipRects(const ClipRectsContext&, ClipRects&) const;
 
-private:
-    void setClipRect(const ClipRectsContext&, const ClipRectComputationState&) const;
-    void addClipsFromThisObject(const ClipRectsContext&, ClipRects&) const;
-    void updateClipRectBasedOnPosition(ClipRects*) const;
+    DeprecatedPaintLayer* clippingRootForPainting() const;
 
-    ClipRect uncachedBackgroundClipRect(const ClipRectsContext&) const;
-    void uncachedCalculateClipRects(const ClipRectsContext&, ClipRects&) const;
+    ClipRectsCache& cache() const
+    {
+        if (!m_cache)
+            m_cache = adoptPtr(new ClipRectsCache);
+        return *m_cache;
+    }
 
     bool shouldRespectOverflowClip(const ClipRectsContext&) const;
 
     // FIXME: Could this be a LayoutBox?
     LayoutBoxModelObject& m_layoutObject;
-    mutable OwnPtr<ClipRect> m_clips[NumberOfClipRectsCacheSlots];
+    mutable OwnPtr<ClipRectsCache> m_cache;
 };
 
 } // namespace blink