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

cc/switches.cc

 // 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.
 
 #include "cc/switches.h"
 
 namespace cc {
 namespace switches {
 
 // On platforms where checkerboards are used, prefer background colors instead
 // of checkerboards.
 const char kBackgroundColorInsteadOfCheckerboard[] =
     "background-color-instead-of-checkerboard";
 
 const char kDisableThreadedAnimation[]      = "disable-threaded-animation";
 
 // Paint content on the compositor thread instead of the main thread.
 const char kEnableImplSidePainting[] = "enable-impl-side-painting";
 
 const char kEnablePartialSwap[]             = "enable-partial-swap";
 
 const char kEnablePerTilePainting[]         = "enable-per-tile-painting";
 
 // Enables an alternative pinch-zoom gesture support, via the threaded
 // compositor.
 const char kEnablePinchInCompositor[]       = "enable-pinch-in-compositor";
 
+// Number of worker threads used to rasterize content.
+const char kNumRasterThreads[] = "num-raster-threads";
+
 // Show rects in the HUD around layers whose properties have changed.
 const char kShowPropertyChangedRects[] = "show-property-changed-rects";
 
 // Show rects in the HUD around damage as it is recorded into each render
 // surface.
 const char kShowSurfaceDamageRects[] = "show-surface-damage-rects";
 
 // Show rects in the HUD around the screen-space transformed bounds of every
 // layer.
 const char kShowScreenSpaceRects[] = "show-screenspace-rects";
 
 // Show rects in the HUD around the screen-space transformed bounds of every
 // layer's replica, when they have one.
 const char kShowReplicaScreenSpaceRects[] = "show-replica-screenspace-rects";
 
 // Show rects in the HUD wherever something is known to be drawn opaque and is
 // considered occluding the pixels behind it.
 const char kShowOccludingRects[] = "show-occluding-rects";
 
 // Show rects in the HUD wherever something is not known to be drawn opaque and
 // is not considered to be occluding the pixels behind it.
 const char kShowNonOccludingRects[] = "show-nonoccluding-rects";
 
 // Show metrics about overdraw in about:tracing recordings, such as the number
 // of pixels culled, and the number of pixels drawn, for each frame.
 const char kTraceOverdraw[] = "trace-overdraw";
 
 }  // namespace switches
 }  // namespace cc