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

cc/base/rolling_time_delta_history.cc

 // 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.
 
 #include <cmath>
 
 #include "cc/base/rolling_time_delta_history.h"
 
 namespace cc {
 
 RollingTimeDeltaHistory::RollingTimeDeltaHistory(size_t max_size)
     : max_size_(max_size) {}
 
 RollingTimeDeltaHistory::~RollingTimeDeltaHistory() {}
 
 void RollingTimeDeltaHistory::InsertSample(base::TimeDelta time) {
   if (max_size_ == 0)
     return;
 
   if (sample_set_.size() == max_size_) {
     sample_set_.erase(chronological_sample_deque_.front());
     chronological_sample_deque_.pop_front();
   }
 
   TimeDeltaMultiset::iterator it = sample_set_.insert(time);
   chronological_sample_deque_.push_back(it);
 }
 
+size_t RollingTimeDeltaHistory::SampleCount() {
+  return sample_set_.size();
+}
+
 void RollingTimeDeltaHistory::Clear() {
   chronological_sample_deque_.clear();
   sample_set_.clear();
 }
 
 base::TimeDelta RollingTimeDeltaHistory::Percentile(double percent) const {
   if (sample_set_.size() == 0)
     return base::TimeDelta();
 
   double fraction = percent / 100.0;
@@ skipping 15 matching lines @@
     return *it;
   }
 
   TimeDeltaMultiset::const_iterator it = sample_set_.begin();
   for (size_t i = 0; i < num_smaller_samples; i++)
     it++;
   return *it;
 }
 
 }  // namespace cc