cc: Add experimental --num-raster-threads option.

cc/switches.h

 // Copyright (c) 2012 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.
 
 // Defines all the "cc" command-line switches.
 
 #ifndef CC_SWITCHES_H_
 #define CC_SWITCHES_H_
 
 #include "cc/cc_export.h"
 
 // Since cc is used from the render process, anything that goes here also needs
 // to be added to render_process_host_impl.cc.
 
 namespace cc {
 namespace switches {
 
 CC_EXPORT extern const char kBackgroundColorInsteadOfCheckerboard[];
 CC_EXPORT extern const char kDisableThreadedAnimation[];
 CC_EXPORT extern const char kEnableImplSidePainting[];
 CC_EXPORT extern const char kEnablePartialSwap[];
 CC_EXPORT extern const char kEnablePerTilePainting[];
 CC_EXPORT extern const char kEnablePinchInCompositor[];
 CC_EXPORT extern const char kJankInsteadOfCheckerboard[];
+CC_EXPORT extern const char kNumRasterThreads[];
 CC_EXPORT extern const char kShowPropertyChangedRects[];
 CC_EXPORT extern const char kShowSurfaceDamageRects[];
 CC_EXPORT extern const char kShowScreenSpaceRects[];
 CC_EXPORT extern const char kShowReplicaScreenSpaceRects[];
 CC_EXPORT extern const char kShowOccludingRects[];
 CC_EXPORT extern const char kShowNonOccludingRects[];
 CC_EXPORT extern const char kTraceOverdraw[];
 
 }  // namespace switches
 }  // namespace cc
 
 #endif  // CC_SWITCHES_H_