Remove offscreen compositor contexts.

cc/trees/single_thread_proxy.h

Index: cc/trees/single_thread_proxy.h
diff --git a/cc/trees/single_thread_proxy.h b/cc/trees/single_thread_proxy.h
index 0f86673ed8182357c47a20ed71ae3ad9b7f757b4..df1113e97ca71ef769d2790852d1c6ee7859c94f 100644
--- a/cc/trees/single_thread_proxy.h
+++ b/cc/trees/single_thread_proxy.h
@@ -94,8 +94,7 @@ class SingleThreadProxy : public Proxy, LayerTreeHostImplClient {
                           bool for_readback,
                           LayerTreeHostImpl::FrameData* frame);
   void DoCommit(scoped_ptr<ResourceUpdateQueue> queue);
-  bool DoComposite(scoped_refptr<ContextProvider> offscreen_context_provider,
-                   base::TimeTicks frame_begin_time,
+  bool DoComposite(base::TimeTicks frame_begin_time,
                    const gfx::Rect& device_viewport_damage_rect,
                    bool for_readback,
                    LayerTreeHostImpl::FrameData* frame);
@@ -107,7 +106,6 @@ class SingleThreadProxy : public Proxy, LayerTreeHostImplClient {
   // Accessed on main thread only.
   LayerTreeHost* layer_tree_host_;
   LayerTreeHostSingleThreadClient* client_;
-  bool created_offscreen_context_provider_;
 
   // Used on the Thread, but checked on main thread during
   // initialization/shutdown.