Move RenderStats enumeration out of gpu_benchmarking_extension.

cc/rendering_stats.h

 // Copyright 2012 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_RENDERING_STATS_H_
 #define CC_RENDERING_STATS_H_
 
 #include "base/basictypes.h"
 #include "cc/cc_export.h"
 
 namespace cc {
 
 struct CC_EXPORT RenderingStats {
     // FIXME: Rename these to animationFrameCount and screenFrameCount, crbug.com/138641.
     int64 numAnimationFrames;
     int64 numFramesSentToScreen;
     int64 droppedFrameCount;
     double totalPaintTimeInSeconds;
     double totalRasterizeTimeInSeconds;
     double totalCommitTimeInSeconds;
     int64 totalCommitCount;
     int64 totalPixelsPainted;
     int64 totalPixelsRasterized;
     int64 numImplThreadScrolls;
     int64 numMainThreadScrolls;
     int64 numLayersInLayerTree;
+    // Note: when adding new members, please remember to update enumerateFields
+    // in rendering_stats.cc.
 
     RenderingStats();
+
+    // In conjunction with enumerateFields, this allows the embedder to
+    // enumerate the values in this structure without
+    // having to embed references to its specific member variables. This
+    // simplifies the addition of new fields to this type.
+    class Enumerator {
+    public:
+        virtual void addInt64(const char* name, int64 value) = 0;
+        virtual void addDouble(const char* name, double value) = 0;
+
+    protected:
+        virtual ~Enumerator() { }
+    };
+
+    // Outputs the fields in this structure to the provided enumerator.
+    void enumerateFields(Enumerator* enumerator) const;
 };
 
 }  // namespace cc
 
 #endif  // CC_RENDERING_STATS_H_