Use a struct for cc::Surface ids for more type safety

cc/surfaces/surface_id.h

+// Copyright 2014 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.
+
+#ifndef CC_SURFACES_SURFACE_ID_H_
+#define CC_SURFACES_SURFACE_ID_H_
+
+namespace cc {
+
+struct SurfaceId {
+  SurfaceId() : id(0) {}
+  explicit SurfaceId(int id) : id(id) {}
+
+  bool is_null() const { return id == 0; }
+
+  int id;
+};
+
+inline bool operator==(const SurfaceId& a, const SurfaceId& b) {
+  return a.id == b.id;
+}
+
+inline bool operator!=(const SurfaceId& a, const SurfaceId& b) {
+  return !(a == b);
+}
+
+}  // namespace cc
+
+#endif  // CC_SURFACES_SURFACE_ID_H_