Remove external begin frame source parameter and settings

cc/trees/proxy_impl.h

Index: cc/trees/proxy_impl.h
diff --git a/cc/trees/proxy_impl.h b/cc/trees/proxy_impl.h
index 2ade6196b0f3e110206096b690fe2ef0d1b7fc31..3ef3534ac25a571191222f3207e7bf7f5b3a4c3f 100644
--- a/cc/trees/proxy_impl.h
+++ b/cc/trees/proxy_impl.h
@@ -26,8 +26,7 @@ class CC_EXPORT ProxyImpl : public NON_EXPORTED_BASE(LayerTreeHostImplClient),
  public:
   ProxyImpl(ChannelImpl* channel_impl,
             LayerTreeHostInProcess* layer_tree_host,
-            TaskRunnerProvider* task_runner_provider,
-            std::unique_ptr<BeginFrameSource> external_begin_frame_source);
+            TaskRunnerProvider* task_runner_provider);
   ~ProxyImpl() override;
 
   // Virtual for testing.
@@ -136,8 +135,6 @@ class CC_EXPORT ProxyImpl : public NON_EXPORTED_BASE(LayerTreeHostImplClient),
 
   DelayedUniqueNotifier smoothness_priority_expiration_notifier_;
 
-  std::unique_ptr<BeginFrameSource> external_begin_frame_source_;
-
   RenderingStatsInstrumentation* rendering_stats_instrumentation_;
 
   std::unique_ptr<LayerTreeHostImpl> layer_tree_host_impl_;