Reland "Add new latency_info for tracking browser composite time."

cc/base/rolling_time_delta_history.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_BASE_ROLLING_TIME_DELTA_HISTORY_H_
 #define CC_BASE_ROLLING_TIME_DELTA_HISTORY_H_
 
 #include <deque>
 #include <set>
 
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
 
 namespace cc {
 
 // Stores a limited number of samples. When the maximum size is reached, each
 // insertion results in the deletion of the oldest remaining sample.
 class CC_EXPORT RollingTimeDeltaHistory {
  public:
   explicit RollingTimeDeltaHistory(size_t max_size);
 
   ~RollingTimeDeltaHistory();
 
   void InsertSample(base::TimeDelta time);
 
+  size_t SampleCount();

[Sami, 2015/01/06 12:21:40]

drive-by nit: const

+
   void Clear();
 
   // Returns the smallest sample that is greater than or equal to the specified
   // percent of samples. If there aren't any samples, returns base::TimeDelta().
   base::TimeDelta Percentile(double percent) const;
 
  private:
   typedef std::multiset<base::TimeDelta> TimeDeltaMultiset;
 
   TimeDeltaMultiset sample_set_;
   std::deque<TimeDeltaMultiset::iterator> chronological_sample_deque_;
   size_t max_size_;
 
   DISALLOW_COPY_AND_ASSIGN(RollingTimeDeltaHistory);
 };
 
 }  // namespace cc
 
 #endif  // CC_BASE_ROLLING_TIME_DELTA_HISTORY_H_