cc: Implement overdraw feedback debugging feature.

cc/base/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/base/switches.h"
 
 #include "base/command_line.h"
 
 namespace cc {
 namespace switches {
@@ skipping 80 matching lines @@
 
 // Show rects in the HUD around the screen-space transformed bounds of every
 // layer.
 const char kShowScreenSpaceRects[] = "show-screenspace-rects";
 const char kUIShowScreenSpaceRects[] = "ui-show-screenspace-rects";
 
 // Switches cc machinery to use layer lists instead of layer trees
 const char kEnableLayerLists[] = "enable-layer-lists";
 const char kUIEnableLayerLists[] = "ui-enable-layer-lists";
 
+// Visualize overdraw by color-coding elements based on if they have other
+// elements drawn underneath. This is good for showing where the UI might be
+// doing more rendering work than necessary. The colors are hinting at the
+// amount of overdraw on your screen for each pixel, as follows:
+//
+// True color: No overdraw.
+// Blue: Overdrawn once.
+// Green: Overdrawn twice.
+// Pink: Overdrawn three times.
+// Red: Overdrawn four or more times.
+const char kShowOverdrawFeedback[] = "show-overdraw-feedback";
+
 // Prevents the layer tree unit tests from timing out.
 const char kCCLayerTreeTestNoTimeout[] = "cc-layer-tree-test-no-timeout";
 
 // Increases timeout for memory checkers.
 const char kCCLayerTreeTestLongTimeout[] = "cc-layer-tree-test-long-timeout";
 
 // Makes pixel tests write their output instead of read it.
 const char kCCRebaselinePixeltests[] = "cc-rebaseline-pixeltests";
 
 }  // namespace switches
 }  // namespace cc