Add concurrency check to HistogramSnapshotManager.

base/metrics/histogram_snapshot_manager.h

 // 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.
 
 #ifndef BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
 #define BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
 
 #include <stdint.h>
 
+#include <atomic>
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_base.h"
-#include "base/threading/thread_checker.h"
 
 namespace base {
 
 class HistogramSamples;
 class HistogramFlattener;
 
 // HistogramSnapshotManager handles the logistics of gathering up available
 // histograms for recording either to disk or for transmission (such as from
 // renderer to browser, or from browser to UMA upload). Since histograms can sit
 // in memory for an extended period of time, and are vulnerable to memory
@@ skipping 41 matching lines @@
     // The set of inconsistencies (flags) already seen for the histogram.
     // See HistogramBase::Inconsistency for values.
     uint32_t inconsistencies = 0;
   };
 
   // Capture and hold samples from a histogram. This does all the heavy
   // lifting for PrepareDelta() and PrepareAbsolute().
   void PrepareSamples(const HistogramBase* histogram,
                       std::unique_ptr<HistogramSamples> samples);
 
+  // |histogram_flattener_| handles the logistics of recording the histogram
+  // deltas.
+  HistogramFlattener* const histogram_flattener_;  // Weak.
+
   // For histograms, track what has been previously seen, indexed
   // by the hash of the histogram name.
   std::map<uint64_t, SampleInfo> known_histograms_;
 
-  // |histogram_flattener_| handles the logistics of recording the histogram
-  // deltas.
-  HistogramFlattener* histogram_flattener_;  // Weak.
-
-  ThreadChecker thread_checker_;
+  // A flag indicating if a thread is currently doing an operation. This is
+  // used to check against concurrent access which is not supported. A Thread-
+  // Checker is not sufficient because it may be guarded by at outside lock
+  // (as is the case with cronet).
+  std::atomic<bool> is_active_;
 
   DISALLOW_COPY_AND_ASSIGN(HistogramSnapshotManager);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_