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

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index 323039f5e699ea828dee5c83b4f410e282a8f955..2a3d3753e6fdc0cb9a318eec18e8547be10a12fa 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -537,8 +537,9 @@ void RenderWidgetCompositor::ApplyScrollAndScale(gfx::Vector2d scroll_delta,
   widget_->webwidget()->applyScrollAndScale(scroll_delta, page_scale);
 }
 
-scoped_ptr<cc::OutputSurface> RenderWidgetCompositor::CreateOutputSurface() {
-  return widget_->CreateOutputSurface();
+scoped_ptr<cc::OutputSurface> RenderWidgetCompositor::CreateOutputSurface(
+    bool fallback) {
+  return widget_->CreateOutputSurface(fallback);
 }
 
 void RenderWidgetCompositor::DidInitializeOutputSurface(bool success) {