Merge subprocess metrics into global StatisticsRecorder.

base/metrics/persistent_histogram_allocator.h

Index: base/metrics/persistent_histogram_allocator.h
diff --git a/base/metrics/persistent_histogram_allocator.h b/base/metrics/persistent_histogram_allocator.h
index 8df45f2813ae6899ad9bf6c294ad64ee477855c1..c2ddca0c7803f6aa946bc583ded3c2ddb4fc0e21 100644
--- a/base/metrics/persistent_histogram_allocator.h
+++ b/base/metrics/persistent_histogram_allocator.h
@@ -248,6 +248,11 @@ class BASE_EXPORT PersistentHistogramAllocator {
   // True, forgetting it otherwise.
   void FinalizeHistogram(Reference ref, bool registered);
 
+  // Merges the data in a persistent histogram with one held globally by the
+  // StatisticsRecorder, updating the "logged" samples within the passed
+  // object so that repeated merges are allowed.
+  void MergeHistogramToStatisticsRecorder(HistogramBase* histogram);
+
   // Returns the object that manages the persistent-sample-map records for a
   // given |id|. Only one |user| of this data is allowed at a time. This does
   // an automatic Acquire() on the records. The user must call Release() on