Remove CompositeAndReadback from LayerTreeHost(Impl) and the Proxys.

cc/scheduler/draw_result.h

 // Copyright 2014 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_SCHEDULER_DRAW_RESULT_H_
 #define CC_SCHEDULER_DRAW_RESULT_H_
 
 namespace cc {
 
 enum DrawResult {
-    INVALID_RESULT,
-    DRAW_SUCCESS,
-    DRAW_ABORTED_CHECKERBOARD_ANIMATIONS,
-    DRAW_ABORTED_MISSING_HIGH_RES_CONTENT,
-    DRAW_ABORTED_CANT_READBACK,
-    DRAW_ABORTED_CONTEXT_LOST,
-    DRAW_ABORTED_CANT_DRAW,
+  INVALID_RESULT,
+  DRAW_SUCCESS,
+  DRAW_ABORTED_CHECKERBOARD_ANIMATIONS,
+  DRAW_ABORTED_MISSING_HIGH_RES_CONTENT,
+  // TODO(danakj): Remove this.
+  DRAW_ABORTED_CANT_READBACK,
+  DRAW_ABORTED_CONTEXT_LOST,
+  DRAW_ABORTED_CANT_DRAW,
 };
 
 }  // namespace cc
 
 #endif  // CC_SCHEDULER_DRAW_RESULT_H_