Add a flag to allow renderer to use software compositor when GL compositor doesn't work.

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index f36bf461b54102e805e787928d6eeb31198ba31c..37b63100ed3a66efb17c87ba24bb1bc5aee659cd 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -736,7 +736,7 @@ void Compositor::Layout() {
   disable_schedule_composite_ = false;
 }
 
-scoped_ptr<cc::OutputSurface> Compositor::CreateOutputSurface() {
+scoped_ptr<cc::OutputSurface> Compositor::CreateOutputSurface(bool fallback) {
   return make_scoped_ptr(
       ContextFactory::GetInstance()->CreateOutputSurface(this));
 }