CC Animation: Use ElementId to attach CC animation players.

cc/test/test_element_id.h

Index: cc/test/test_element_id.h
diff --git a/cc/test/test_element_id.h b/cc/test/test_element_id.h
new file mode 100644
index 0000000000000000000000000000000000000000..4f3e1c8e56fcfaa4c53f4541374a6669bf77d0f7
--- /dev/null
+++ b/cc/test/test_element_id.h
@@ -0,0 +1,16 @@
+// Copyright (c) 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_TEST_TEST_ELEMENT_ID_H_
+#define CC_TEST_TEST_ELEMENT_ID_H_
+
+#include "cc/trees/element_id.h"
+
+namespace cc {
+
+ElementId NextTestElementId();
+
+}  // namespace cc
+
+#endif  // CC_TEST_TEST_ELEMENT_ID_H_