Reorganize histograms for persistence.

base/test/histogram_tester.cc

Index: base/test/histogram_tester.cc
diff --git a/base/test/histogram_tester.cc b/base/test/histogram_tester.cc
index 09b4ef30ee3aa6863014db96e136b11b7274ca30..3e0f2b88ca8559dcadde11da1972394324f1ab99 100644
--- a/base/test/histogram_tester.cc
+++ b/base/test/histogram_tester.cc
@@ -6,6 +6,7 @@
 
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_samples.h"
+#include "base/metrics/metrics_hashes.h"
 #include "base/metrics/sample_map.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/stl_util.h"
@@ -122,7 +123,8 @@ scoped_ptr<HistogramSamples> HistogramTester::GetHistogramSamplesSinceCreation(
   // creates empty samples in the absence of the histogram, rather than
   // returning null.
   if (!histogram)
-    return scoped_ptr<HistogramSamples>(new SampleMap);
+    return scoped_ptr<HistogramSamples>(
+        new SampleMap(metrics::HashMetricName(histogram_name)));
   scoped_ptr<HistogramSamples> named_samples(histogram->SnapshotSamples());
   auto original_samples_it = histograms_snapshot_.find(histogram_name);
   if (original_samples_it != histograms_snapshot_.end())