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

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index addee73ae59aa5961b65b3b7472644a25203fe45..31cfd6053e8c607ee458ebbb7ac089eba949ad26 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -394,8 +394,8 @@ class COMPOSITOR_EXPORT Compositor
   virtual void Layout() OVERRIDE;
   virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
                                    float page_scale) OVERRIDE {}
-  virtual scoped_ptr<cc::OutputSurface>
-      CreateOutputSurface() OVERRIDE;
+  virtual scoped_ptr<cc::OutputSurface> CreateOutputSurface(bool fallback)
+      OVERRIDE;
   virtual void DidInitializeOutputSurface(bool success) OVERRIDE {}
   virtual void WillCommit() OVERRIDE {}
   virtual void DidCommit() OVERRIDE;