Remove external begin frame source parameter and settings

cc/trees/proxy.h

Index: cc/trees/proxy.h
diff --git a/cc/trees/proxy.h b/cc/trees/proxy.h
index fd82d809b7259e89807cd192cce3e28ea045678c..53381d9dfe7b020629e5a54109bb3846bc26e7c0 100644
--- a/cc/trees/proxy.h
+++ b/cc/trees/proxy.h
@@ -65,9 +65,9 @@ class CC_EXPORT Proxy {
   virtual bool BeginMainFrameRequested() const = 0;
 
   // Must be called before using the proxy.
-  virtual void Start(
-      std::unique_ptr<BeginFrameSource> external_begin_frame_source) = 0;
-  virtual void Stop() = 0;   // Must be called before deleting the proxy.
+  virtual void Start() = 0;
+  // Must be called before deleting the proxy.
+  virtual void Stop() = 0;
 
   virtual void SetMutator(std::unique_ptr<LayerTreeMutator> mutator) = 0;