Merge multiple histogram snapshots into single one for reporting.

components/metrics/metrics_service.h

Index: components/metrics/metrics_service.h
diff --git a/components/metrics/metrics_service.h b/components/metrics/metrics_service.h
index 8d81484da9896ad8c643930db52730da2b8b3a1b..3b71571f183b77103fb63f69588ff17cf8f89c2b 100644
--- a/components/metrics/metrics_service.h
+++ b/components/metrics/metrics_service.h
@@ -9,6 +9,7 @@
 #define COMPONENTS_METRICS_METRICS_SERVICE_H_
 
 #include <map>
+#include <set>
 #include <string>
 #include <vector>
 
@@ -104,6 +105,8 @@ class MetricsService : public base::HistogramFlattener {
     SHUTDOWN_COMPLETE = 700,
   };
 
+  typedef std::set<base::HistogramBase*> HistogramSet;
+
   // Creates the MetricsService with the given |state_manager|, |client|, and
   // |local_state|.  Does not take ownership of the paramaters; instead stores
   // a weak pointer to each. Caller should ensure that the parameters are valid
@@ -296,21 +299,14 @@ class MetricsService : public base::HistogramFlattener {
 
   // A class for iterating over the histograms in persistent memory segments.
   class PersistentHistogramIterator {
-    // This class provides a reference-counted pointer to a histogram which
-    // is necessary for histogram objects that are dynamically generated
-    // (generally pointing to persistent memory) and to be owned by an STL
-    // iterator which, by necessity, must be copyable.
-    class HistogramPointer : public base::RefCounted<HistogramPointer> {
-     public:
-      HistogramPointer(base::HistogramBase* h) : histogram_(h) {}
-      base::HistogramBase* get() { return histogram_.get(); }
-
-     private:
-      scoped_ptr<base::HistogramBase> histogram_;
-    };
-
    public:
-    PersistentHistogramIterator(AllocatorSet& allocators,
+    // The |found_histograms| set will be loaded with pointers to all the
+    // histograms found during iteration. This is important because users
+    // of the iterator may expect the returned histograms to live longer
+    // than a particular iteration step. The caller must delete these
+    // if necessary.
+    PersistentHistogramIterator(HistogramSet* found_histograms,
+                                AllocatorSet& allocators,
                                 AllocatorSet::iterator pos);
 
     PersistentHistogramIterator& operator++();
@@ -329,7 +325,7 @@ class MetricsService : public base::HistogramFlattener {
              histogram_iter_ != rhs.histogram_iter_;
     }
     base::HistogramBase* operator*() {
-      return current_histogram_->get();
+      return current_histogram_;
     }
 
    private:
@@ -337,9 +333,8 @@ class MetricsService : public base::HistogramFlattener {
     AllocatorSet::iterator allocator_iter_;
     base::PersistentMemoryAllocator::Iterator histogram_iter_;
 
-    // STL iterators must be copyable so a regular scoped_ptr is not
-    // sufficient as it doesn't allow such. A ref-counted one is needed.
-    scoped_refptr<HistogramPointer> current_histogram_;
+    HistogramSet* found_histograms_;
+    base::HistogramBase* current_histogram_;
   };
 
   typedef std::vector<SyntheticTrialGroup> SyntheticTrialGroups;
@@ -483,7 +478,7 @@ class MetricsService : public base::HistogramFlattener {
   void SkipAndDiscardUpload();
 
   // Begin and End iterators for going through all the metrics under management.
-  PersistentHistogramIterator persistent_begin();
+  PersistentHistogramIterator persistent_begin(HistogramSet* found);
   PersistentHistogramIterator persistent_end();
 
   // Manager for the various in-flight logs.