Improve UMA tests; improve no-op reconcilor; new reconcilor test.

base/test/statistics_delta_reader.h

Index: base/test/statistics_delta_reader.h
diff --git a/base/test/statistics_delta_reader.h b/base/test/statistics_delta_reader.h
index 4921d61d076a8ca68a40bf625574d69f41e12f7c..26d87c5b0ad3163ef940ff5ed646c5ebeb9ea3b6 100644
--- a/base/test/statistics_delta_reader.h
+++ b/base/test/statistics_delta_reader.h
@@ -17,6 +17,10 @@ class HistogramSamples;
 
 // This class acts as a differential reader for histogram samples, enabling
 // tests to check that metrics were recorded as they should be.
+//
+// This class is DEPRECATED.
+// TODO(mlerman): Remove all references to this class with UMAHistogramHelper
+// references. crbug.com/384011
 class StatisticsDeltaReader {
  public:
   StatisticsDeltaReader();