Improve performance of GeometryMapper cache.

third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h

Index: third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h b/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h
index 76844fb8d94561ee2542d86cc923ad7a799f78c9..50b68837d11559eebdd6cc63fbff019286248fb2 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h
@@ -188,6 +188,9 @@ class PLATFORM_EXPORT TransformPaintPropertyNode
 
   String toString() const;
 
+  // Clears all transform caches (see getTransformCache()).
+  static void clearCache();
+
  private:
   TransformPaintPropertyNode(
       PassRefPtr<const TransformPaintPropertyNode> parent,
@@ -207,6 +210,31 @@ class PLATFORM_EXPORT TransformPaintPropertyNode
         m_compositorElementId(compositorElementId),
         m_scroll(scroll) {}
 
+  struct TransformCacheEntry {
+    const TransformPaintPropertyNode* ancestorNode;
+    TransformationMatrix toAncestor;
+    TransformCacheEntry(const TransformPaintPropertyNode* ancestorNodeArg,
+                        const TransformationMatrix& toAncestorArg)
+        : ancestorNode(ancestorNodeArg), toAncestor(toAncestorArg) {}
+  };
+
+  // For access to getCachedTransform() and setCachedTransform.
+  friend class GeometryMapper;
+  friend class GeometryMapperTest;
+
+  Vector<TransformCacheEntry>* getTransformCacheEntries();
+
+  // Returns the "transformed rect" (see GeometryMapper.h) of |this| in the
+  // space of |ancestorTransform|, if there is one cached. Otherwise returns
+  // null.
+  const TransformationMatrix* getCachedTransform(
+      const TransformPaintPropertyNode* ancestorTransform) const;
+
+  // Stores the "transformed rect" of |this| in the space of |ancestors|,
+  // into a local cache.
+  void setCachedTransform(const TransformPaintPropertyNode* ancestorTransform,
+                          const TransformationMatrix& toAncestor) const;
+
   RefPtr<const TransformPaintPropertyNode> m_parent;
   TransformationMatrix m_matrix;
   FloatPoint3D m_origin;
@@ -215,6 +243,9 @@ class PLATFORM_EXPORT TransformPaintPropertyNode
   CompositingReasons m_directCompositingReasons;
   CompositorElementId m_compositorElementId;
   RefPtr<ScrollPaintPropertyNode> m_scroll;
+
+  std::unique_ptr<Vector<TransformCacheEntry>> m_transformCache;
+  unsigned m_cacheGeneration;
 };
 
 // Redeclared here to avoid ODR issues.