Update from https://crrev.com/333737

base/metrics/histogram_snapshot_manager.cc

 // Copyright (c) 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.
 
 #include "base/metrics/histogram_snapshot_manager.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram_flattener.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/stl_util.h"
 
-using std::map;
-using std::string;
-
 namespace base {
 
 HistogramSnapshotManager::HistogramSnapshotManager(
     HistogramFlattener* histogram_flattener)
     : histogram_flattener_(histogram_flattener) {
   DCHECK(histogram_flattener_);
 }
 
 HistogramSnapshotManager::~HistogramSnapshotManager() {
   STLDeleteValues(&logged_samples_);
@@ skipping 45 matching lines @@
     int old_corruption = inconsistencies_[histogram_name];
     if (old_corruption == (corruption | old_corruption))
       return;  // We've already seen this corruption for this histogram.
     inconsistencies_[histogram_name] |= corruption;
     histogram_flattener_->UniqueInconsistencyDetected(
         static_cast<HistogramBase::Inconsistency>(corruption));
     return;
   }
 
   HistogramSamples* to_log;
-  map<string, HistogramSamples*>::iterator it =
+  std::map<std::string, HistogramSamples*>::iterator it =
       logged_samples_.find(histogram_name);
   if (it == logged_samples_.end()) {
     to_log = snapshot.release();
 
     // This histogram has not been logged before, add a new entry.
     logged_samples_[histogram_name] = to_log;
   } else {
     HistogramSamples* already_logged = it->second;
     InspectLoggedSamplesInconsistency(*snapshot, already_logged);
     snapshot->Subtract(*already_logged);
@@ skipping 15 matching lines @@
 
   histogram_flattener_->InconsistencyDetectedInLoggedCount(discrepancy);
   if (discrepancy > Histogram::kCommonRaceBasedCountMismatch) {
     // Fix logged_samples.
     logged_samples->Subtract(*logged_samples);
     logged_samples->Add(new_snapshot);
   }
 }
 
 }  // namespace base