Add a stat to the smoothness benchmark for avg number of missing tiles.

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 "base/time.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 numLayersDrawn;
+    int64 numMissingTiles;
     // 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;
         virtual void AddInt(const char* name, int value) = 0;
         virtual void AddTimeDeltaInSecondsF(const char* name,
                                             const base::TimeDelta& 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_