Implemented browser side software compositing.

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 4cb912297bb40c16604125d0115971c9ae9e55ac..b20661c3271be3fb98ddc5f44c309b522a007ecc 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -376,7 +376,8 @@ Compositor::Compositor(CompositorDelegate* delegate,
   settings.initialDebugState.showDebugBorders =
       command_line->HasSwitch(switches::kUIShowLayerBorders);
   settings.partialSwapEnabled =
-      command_line->HasSwitch(switches::kUIEnablePartialSwap);
+      command_line->HasSwitch(switches::kUIEnablePartialSwap) ||
+      command_line->HasSwitch(switches::kUIEnableSoftwareCompositing);

[piman, 2013/03/07 00:25:51]

This shouldn't be here. It should be set by SoftwareRenderer if the
OutputSurface isn't capable of partial updates. Maybe adding a cap bit into the
OutputSurface.

[slavi, 2013/03/07 01:48:30]

I found that this is not really necessary since the software renderer doesn't
respect that override at all:
https://code.google.com/p/chromium/codesearch#chromium/src/cc/software_render...

   settings.perTilePaintingEnabled =
       command_line->HasSwitch(switches::kUIEnablePerTilePainting);