Add stream operator for SurfaceId/FrameSinkId/LocalFrameId.

cc/surfaces/surface_id.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/surfaces/surface_id.h"
+
+#include "base/strings/stringprintf.h"
+
+namespace cc {
+
+std::string SurfaceId::ToString() const {
+  return base::StringPrintf("SurfaceId(%s, %s)",
+                            frame_sink_id_.ToString().c_str(),
+                            local_frame_id_.ToString().c_str());
+}
+
+std::ostream& operator<<(std::ostream& out, const SurfaceId& surface_id) {
+  return out << surface_id.ToString();
+}
+
+}  // namespace cc