Improve performance of GeometryMapper cache.

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

Index: third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.cpp b/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.cpp
index 14211fc303085b4f0df91543f71aa0f768526f08..9b767c8c8fced39bc0557e95fa50d4cdf6821f9d 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.cpp
@@ -8,6 +8,11 @@
 
 namespace blink {
 
+// All transform caches invalidate themselves by tracking a local cache
+// generation, and invalidating their cache if their cache generation disagrees
+// with s_clipCacheGeneration.
+static unsigned s_transformCacheGeneration = 0;
+
 // The root of the transform tree. The root transform node references the root
 // scroll node.
 TransformPaintPropertyNode* TransformPaintPropertyNode::root() {
@@ -59,4 +64,46 @@ String TransformPaintPropertyNode::toTreeString() const {
 
 #endif
 
+void TransformPaintPropertyNode::clearCache() {
+  s_transformCacheGeneration++;
+}
+
+Vector<TransformPaintPropertyNode::TransformCacheEntry>*
+TransformPaintPropertyNode::getTransformCacheEntries() {
+  if (m_cacheGeneration != s_transformCacheGeneration || !m_transformCache) {
+    m_transformCache.reset(new Vector<TransformCacheEntry>);
+    m_cacheGeneration = s_transformCacheGeneration;
+  }
+
+  return m_transformCache.get();
+}
+
+const TransformationMatrix* TransformPaintPropertyNode::getCachedTransform(
+    const TransformPaintPropertyNode* ancestorTransform) const {
+  auto* transformCacheEntries =
+      const_cast<TransformPaintPropertyNode*>(this)->getTransformCacheEntries();
+
+  for (const auto& entry : *transformCacheEntries) {
+    if (entry.ancestorNode == ancestorTransform) {
+      return &entry.toAncestor;
+    }
+  }
+  return nullptr;
+}
+
+void TransformPaintPropertyNode::setCachedTransform(
+    const TransformPaintPropertyNode* ancestorTransform,
+    const TransformationMatrix& toAncestor) const {
+  auto* transformCacheEntries =
+      const_cast<TransformPaintPropertyNode*>(this)->getTransformCacheEntries();
+#if DCHECK_IS_ON
+  for (const auto& entry : transformCacheEntries) {
+    if (entry.ancestorNode == ancestorTransform)
+      DCHECK(false);  // There should be no existing entry.
+  }
+#endif
+  transformCacheEntries->push_back(
+      TransformCacheEntry(ancestorTransform, toAncestor));
+}
+
 }  // namespace blink