Mozart: Improve internal scene graph representation.

services/gfx/compositor/graph/scene_label.h

+// 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.
+
+#ifndef SERVICES_GFX_COMPOSITOR_GRAPH_SCENE_LABEL_H_
+#define SERVICES_GFX_COMPOSITOR_GRAPH_SCENE_LABEL_H_
+
+#include <string>
+
+namespace compositor {
+
+// Convenience class for formatting descriptive labels for diagnostics.
+class SceneLabel {
+ public:
+  SceneLabel(uint32_t token, const std::string& label);
+  SceneLabel(const SceneLabel& other);
+  ~SceneLabel();
+
+  // Gets the scene token.
+  uint32_t token() const { return token_; }
+
+  // Gets the user-supplied label of the scene.
+  const std::string& label() const { return label_; }
+
+  // Gets a descriptive label including optional version and node information.
+  std::string FormattedLabel() const;
+  std::string FormattedLabelForVersion(uint32_t version) const;
+  std::string FormattedLabelForNode(uint32_t version, uint32_t node_id) const;
+
+ private:
+  uint32_t const token_;
+  std::string const label_;
+};
+
+}  // namespace compositor
+
+#endif  // SERVICES_GFX_COMPOSITOR_GRAPH_SCENE_LABEL_H_