Fold BeginFrameSource::SetClientReady into AddObserver

cc/test/fake_external_begin_frame_source.h

Index: cc/test/fake_external_begin_frame_source.h
diff --git a/cc/test/fake_external_begin_frame_source.h b/cc/test/fake_external_begin_frame_source.h
index 99dbf56ef1999a3686ce986fae5751c6e6c9ddf0..1653decf8cc86465af54b7859f06d9a28e74bff7 100644
--- a/cc/test/fake_external_begin_frame_source.h
+++ b/cc/test/fake_external_begin_frame_source.h
@@ -17,11 +17,6 @@ class FakeExternalBeginFrameSource
   explicit FakeExternalBeginFrameSource(double refresh_rate);
   ~FakeExternalBeginFrameSource() override;
 
-  bool is_ready() const { return is_ready_; }
-
-  // BeginFrameSource implementation.
-  void SetClientReady() override;
-
   // BeginFrameSourceBase overrides.
   void OnNeedsBeginFramesChanged(bool needs_begin_frames) override;
 
@@ -30,7 +25,6 @@ class FakeExternalBeginFrameSource
 
  private:
   double milliseconds_per_frame_;
-  bool is_ready_;
   base::CancelableClosure begin_frame_task_;
   base::WeakPtrFactory<FakeExternalBeginFrameSource> weak_ptr_factory_;
 };