Support "shared" histograms between processes.

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 <map>
 #include <string>
 
@@ skipping 16 matching lines @@
  public:
   explicit HistogramSnapshotManager(HistogramFlattener* histogram_flattener);
   virtual ~HistogramSnapshotManager();
 
   // Snapshot all histograms, and ask |histogram_flattener_| to record the
   // delta. |flags_to_set| is used to set flags for each histogram.
   // |required_flags| is used to select histograms to be recorded.
   // Only histograms that have all the flags specified by the argument will be
   // chosen. If all histograms should be recorded, set it to
   // |Histogram::kNoFlags|.
-  void PrepareDeltas(HistogramBase::Flags flags_to_set,
-                     HistogramBase::Flags required_flags);
+  template <class ForwardHistogramIterator>
+  void PrepareDeltas(ForwardHistogramIterator begin,
+                     ForwardHistogramIterator end,
+                     HistogramBase::Flags flags_to_set,
+                     HistogramBase::Flags required_flags) {
+    for (ForwardHistogramIterator it = begin; it != end; ++it) {
+      (*it)->SetFlags(flags_to_set);
+      if (((*it)->flags() & required_flags) == required_flags)
+        PrepareDelta(**it);
+    }
+  }
 
  private:
   // Snapshot this histogram, and record the delta.
   void PrepareDelta(const HistogramBase& histogram);
 
   // Try to detect and fix count inconsistency of logged samples.
   void InspectLoggedSamplesInconsistency(
       const HistogramSamples& new_snapshot,
       HistogramSamples* logged_samples);
 
   // For histograms, track what we've already recorded (as a sample for
   // each histogram) so that we can record only the delta with the next log.
   std::map<uint64_t, HistogramSamples*> logged_samples_;
 
   // List of histograms found to be corrupt, and their problems.
   std::map<uint64_t, int> inconsistencies_;
 
   // |histogram_flattener_| handles the logistics of recording the histogram
   // deltas.
   HistogramFlattener* histogram_flattener_;  // Weak.
 
   DISALLOW_COPY_AND_ASSIGN(HistogramSnapshotManager);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_