compositor-worker: cc->blink mutation plumbing

cc/animation/layer_tree_mutations.h

+// Copyright 2016 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.
+
+#ifndef CC_ANIMATION_LAYER_TREE_MUTATIONS_H_
+#define CC_ANIMATION_LAYER_TREE_MUTATIONS_H_
+
+namespace cc {
+
+// Represents a set of mutations. The base class is defined in CC allowing CC
+// to have reference to mutations as it pipes them through to blink. The actual
+// implementation lives in blink where mutations are applied to DOM elements.
+struct LayerTreeMutations {
+  virtual ~LayerTreeMutations() {}
+};
+
+}  // namespace cc
+
+#endif  // CC_ANIMATION_LAYER_TREE_MUTATIONS_H_