compositor-worker: plumb element id and mutable properties

cc/animation/mutable_properties.h

+// Copyright 2015 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_MUTABLE_PROPERTIES_H_
+#define CC_ANIMATION_MUTABLE_PROPERTIES_H_
+
+namespace cc {
+
+enum MutableProperty {
+  kMutablePropertyNone = 0,
+  kMutablePropertyOpacity = 1 << 0,
+  kMutablePropertyScrollLeft = 1 << 1,
+  kMutablePropertyScrollTop = 1 << 2,
+  kMutablePropertyTransform = 1 << 3,
+};
+
+}  // namespace cc
+
+#endif  // CC_ANIMATION_MUTABLE_PROPERTIES_H_