Make SurfaceFactory lifetime match frame_sink_id_ registration in BlimpCompositor

blimp/client/core/compositor/blimp_compositor.h

Index: blimp/client/core/compositor/blimp_compositor.h
diff --git a/blimp/client/core/compositor/blimp_compositor.h b/blimp/client/core/compositor/blimp_compositor.h
index 974f4a291853f5bbf79bb64dc29e6292e6f06dcb..54b95caaeaf10c47b5d45573344ba413d9234bca 100644
--- a/blimp/client/core/compositor/blimp_compositor.h
+++ b/blimp/client/core/compositor/blimp_compositor.h
@@ -214,10 +214,9 @@ class BlimpCompositor : public cc::LayerTreeHostClient,
 
   std::unique_ptr<cc::LayerTreeHostInProcess> host_;
 
-  // The SurfaceFactory is bound to the lifetime of the |proxy_client_|. When
-  // detached, the surface factory will be destroyed.
   std::unique_ptr<cc::SurfaceFactory> surface_factory_;
   base::WeakPtr<BlimpCompositorFrameSinkProxyClient> proxy_client_;
+  bool bound_to_proxy_;
 
   // Whether or not |host_| has asked for a new CompositorFrameSink.
   bool compositor_frame_sink_request_pending_;