Revert of Switch cc::RollingTimeDeltaHistory to use a vector

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 <stddef.h>
 
-#include <algorithm>
 #include <cmath>
 
 #include "cc/base/rolling_time_delta_history.h"
 
 namespace cc {
 
 RollingTimeDeltaHistory::RollingTimeDeltaHistory(size_t max_size)
-    : next_index_(0), max_size_(max_size) {
-  sample_vector_.reserve(max_size_);
-}
+    : max_size_(max_size) {}
 
 RollingTimeDeltaHistory::~RollingTimeDeltaHistory() {}
 
 void RollingTimeDeltaHistory::InsertSample(base::TimeDelta time) {
   if (max_size_ == 0)
     return;
 
-  if (sample_vector_.size() == max_size_) {
-    sample_vector_[next_index_++] = time;
-    if (next_index_ == max_size_)
-      next_index_ = 0;
-  } else {
-    sample_vector_.push_back(time);
+  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);
 }
 
 void RollingTimeDeltaHistory::Clear() {
-  sample_vector_.clear();
-  next_index_ = 0;
+  chronological_sample_deque_.clear();
+  sample_set_.clear();
 }
 
 base::TimeDelta RollingTimeDeltaHistory::Percentile(double percent) const {
-  if (sample_vector_.size() == 0)
+  if (sample_set_.size() == 0)
     return base::TimeDelta();
 
   double fraction = percent / 100.0;
+
   if (fraction <= 0.0)
-    return *std::min_element(sample_vector_.begin(), sample_vector_.end());
+    return *(sample_set_.begin());
 
   if (fraction >= 1.0)
-    return *std::max_element(sample_vector_.begin(), sample_vector_.end());
+    return *(sample_set_.rbegin());
 
   size_t num_smaller_samples =
-      static_cast<size_t>(std::ceil(fraction * sample_vector_.size())) - 1;
+      static_cast<size_t>(std::ceil(fraction * sample_set_.size())) - 1;
 
-  std::vector<base::TimeDelta> v(sample_vector_.begin(), sample_vector_.end());
-  std::nth_element(v.begin(), v.begin() + num_smaller_samples, v.end());
-  return v[num_smaller_samples];
+  if (num_smaller_samples > sample_set_.size() / 2) {
+    size_t num_larger_samples = sample_set_.size() - num_smaller_samples - 1;
+    TimeDeltaMultiset::const_reverse_iterator it = sample_set_.rbegin();
+    for (size_t i = 0; i < num_larger_samples; i++)
+      it++;
+    return *it;
+  }
+
+  TimeDeltaMultiset::const_iterator it = sample_set_.begin();
+  for (size_t i = 0; i < num_smaller_samples; i++)
+    it++;
+  return *it;
 }
 
 }  // namespace cc