Improve performance of GeometryMapper cache.

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

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "platform/graphics/paint/GeometryMapperTransformCache.h"
+
+namespace blink {
+
+// All transform caches invalidate themselves by tracking a local cache
+// generation, and invalidating their cache if their cache generation disagrees
+// with s_transformCacheGeneration.
+static unsigned s_transformCacheGeneration = 0;
+
+GeometryMapperTransformCache::GeometryMapperTransformCache()
+    : m_cacheGeneration(s_transformCacheGeneration) {}
+
+void GeometryMapperTransformCache::clearCache() {
+  s_transformCacheGeneration++;
+}
+
+void GeometryMapperTransformCache::invalidateCacheIfNeeded() {
+  if (m_cacheGeneration != s_transformCacheGeneration) {
+    m_transformCache.clear();
+    m_cacheGeneration = s_transformCacheGeneration;
+  }
+}
+
+const TransformationMatrix* GeometryMapperTransformCache::getCachedTransform(
+    const TransformPaintPropertyNode* ancestorTransform) {
+  invalidateCacheIfNeeded();
+  for (const auto& entry : m_transformCache) {
+    if (entry.ancestorNode == ancestorTransform) {
+      return &entry.toAncestor;
+    }
+  }
+  return nullptr;
+}
+
+void GeometryMapperTransformCache::setCachedTransform(
+    const TransformPaintPropertyNode* ancestorTransform,
+    const TransformationMatrix& matrix) {
+  invalidateCacheIfNeeded();
+#if DCHECK_IS_ON()
+  for (const auto& entry : m_transformCache) {
+    if (entry.ancestorNode == ancestorTransform)
+      DCHECK(false);  // There should be no existing entry.
+  }
+#endif
+  m_transformCache.push_back(TransformCacheEntry(ancestorTransform, matrix));
+}
+
+}  // namespace blink