Add --disable-low-res-tiling. Disable low res tiling to save power.

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 {
 
 const char kDisableThreadedAnimation[] = "disable-threaded-animation";
 
 // Disables layer-edge anti-aliasing in the compositor.
 const char kDisableCompositedAntialiasing[] =
     "disable-composited-antialiasing";
 
 const char kEnableTopControlsPositionCalculation[] =
     "enable-top-controls-position-calculation";
 
+// When using CPU rasterizing generate low resolution tiling. Low res
+// tiles may be displayed during fast scrolls especially on slower devices.
+const char kEnableLowResTiling[] = "enable-low-res-tiling";
+
+// When using CPU rasterizing disable low resolution tiling. This uses
+// less power, particularly during animations, but more white may be seen
+// during fast scrolling especially on slower devices.
+const char kDisableLowResTiling[] = "disable-low-res-tiling";
+
 // The height of the movable top controls.
 const char kTopControlsHeight[] = "top-controls-height";
 
 // Percentage of the top controls need to be hidden before they will auto hide.
 const char kTopControlsHideThreshold[] = "top-controls-hide-threshold";
 
 // Percentage of the top controls need to be shown before they will auto show.
 const char kTopControlsShowThreshold[] = "top-controls-show-threshold";
 
 // Show metrics about overdraw in about:tracing recordings, such as the number
@@ skipping 76 matching lines @@
 // Prevents the layer tree unit tests from timing out.
 const char kCCLayerTreeTestNoTimeout[] = "cc-layer-tree-test-no-timeout";
 
 // Makes pixel tests write their output instead of read it.
 const char kCCRebaselinePixeltests[] = "cc-rebaseline-pixeltests";
 
 // Disable touch hit testing in the compositor.
 const char kDisableCompositorTouchHitTesting[] =
     "disable-compositor-touch-hit-testing";
 
+bool IsLowResTilingEnabled() {

[piman, 2014/03/13 00:52:00]

Nit: this is only used in the renderer. Could this be a bool on
RenderThreadImpl, similar to other related state? Like e.g.
RenderThreadImpl::is_impl_side_painting_enabled()
That way we don't have to parse strings every time we create a compositor. Also
maybe one day we won't have to pass a gigantic command line to the renderer.

+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+
+  if (command_line.HasSwitch(switches::kDisableLowResTiling))
+    return false;
+  else if (command_line.HasSwitch(switches::kEnableLowResTiling))
+    return true;
+
+  return true;
+}
+
 }  // namespace switches
 }  // namespace cc