Measuring data use of different ModelTypes in Sync Service.

sync/util/data_type_histogram.h

Index: sync/util/data_type_histogram.h
diff --git a/sync/util/data_type_histogram.h b/sync/util/data_type_histogram.h
index 0f7e6a99e594fb5d678ae8a4d4a3a875a3dc3584..20a6f8a99bbaa0e679d60a29a273948ebdd2708a 100644
--- a/sync/util/data_type_histogram.h
+++ b/sync/util/data_type_histogram.h
@@ -5,10 +5,18 @@
 #ifndef SYNC_UTIL_DATA_TYPE_HISTOGRAM_H_
 #define SYNC_UTIL_DATA_TYPE_HISTOGRAM_H_
 
-#include "base/metrics/histogram.h"
+#include <string>
+
+#include "base/metrics/histogram_macros.h"
 #include "base/time/time.h"
 #include "sync/internal_api/public/base/model_type.h"
 
+// This function adds |value| to |sample| bucket of histogram |name|. |value|
+// should be greater or equal to 1 and |name| can be variable. DataTypes are
+// mapped to proper |sample| bucket by using ModelTypeToHistogramInt() function.
+// So different DataTypes play the role of different buckets in this histogram.
+void SyncRecordDatatypeBin(const std::string& name, int sample, int value);
+
 // For now, this just implements UMA_HISTOGRAM_LONG_TIMES. This can be adjusted
 // if we feel the min, max, or bucket count amount are not appropriate.
 #define SYNC_FREQ_HISTOGRAM(name, time) UMA_HISTOGRAM_CUSTOM_TIMES( \