Replace usage of SurfaceId's client_id with FrameSinkId

cc/trees/surface_sequence_generator.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <cc/trees/surface_sequence_generator.h>
 #include "cc/surfaces/surface_sequence.h"
 
 namespace cc {
 
 SurfaceSequenceGenerator::SurfaceSequenceGenerator()
-    : surface_client_id_(0u), next_surface_sequence_(1u) {}
+    : next_surface_sequence_(1u) {}
 
 SurfaceSequenceGenerator::~SurfaceSequenceGenerator() = default;
 
 SurfaceSequence SurfaceSequenceGenerator::CreateSurfaceSequence() {
-  return SurfaceSequence(surface_client_id_, next_surface_sequence_++);
+  return SurfaceSequence(frame_sink_id_, next_surface_sequence_++);
 }
 
 }  // namespace cc