Cache the absolute bounding box rect on RenderLayer.

Source/core/rendering/RenderLayer.h

Index: Source/core/rendering/RenderLayer.h
diff --git a/Source/core/rendering/RenderLayer.h b/Source/core/rendering/RenderLayer.h
index cf9654aa369d9899df8cf2db658482a291ef91a7..391dddc3d5eb28cd9ee685c75830c6fbddc6cf21 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -299,10 +299,6 @@ public:
 
     // Bounding box relative to some ancestor layer. Pass offsetFromRoot if known.
     LayoutRect boundingBox(const RenderLayer* rootLayer, CalculateLayerBoundsFlags = 0, const LayoutPoint* offsetFromRoot = 0) const;
-    // Bounding box in the coordinates of this layer.
-    LayoutRect localBoundingBox(CalculateLayerBoundsFlags = 0) const;
-    // Pixel snapped bounding box relative to the root.
-    IntRect absoluteBoundingBox() const;
 
     // Bounds used for layer overlap testing in RenderLayerCompositor.
     LayoutRect overlapBounds() const { return overlapBoundsIncludeChildren() ? calculateLayerBounds(this) : localBoundingBox(); }
@@ -479,7 +475,15 @@ public:
 
     bool hasDirectReasonsForCompositing() const { return compositingReasons() & CompositingReasonComboAllDirectReasons; }
 
+    const IntRect& cachedAbsoluteBoundingBox() { ASSERT(!m_needsToRecomputeBounds); return m_cachedAbsoluteBoundingBox; }
+    void setAbsoluteBoundingBoxForOverlap(const IntRect&);
+    void clearNeedsToRecomputeBounds();
+    bool needsToRecomputeBounds() { return m_needsToRecomputeBounds; }
+
 private:
+    // Bounding box in the coordinates of this layer.
+    LayoutRect localBoundingBox(CalculateLayerBoundsFlags = 0) const;
+
     bool hasOverflowControls() const;
 
     void setIsUnclippedDescendant(bool isUnclippedDescendant) { m_isUnclippedDescendant = isUnclippedDescendant; }
@@ -682,6 +686,7 @@ private:
     const unsigned m_canSkipRepaintRectsUpdateOnScroll : 1;
 
     unsigned m_hasFilterInfo : 1;
+    unsigned m_needsToRecomputeBounds : 1;
 
     RenderLayerModelObject* m_renderer;
 
@@ -704,6 +709,8 @@ private:
     LayoutUnit m_staticInlinePosition;
     LayoutUnit m_staticBlockPosition;
 
+    IntRect m_cachedAbsoluteBoundingBox;

[esprehn, 2014/03/21 23:28:01]

m_absoluteBoundingBox ? cached seems like a detail.

[ojan, 2014/03/22 00:25:43]

I guess. I wanted to distinguish from boundingBox.

+
     OwnPtr<TransformationMatrix> m_transform;
 
     // Pointer to the enclosing RenderLayer that caused us to be paginated. It is 0 if we are not paginated.