Reland: [Sync] Record sync memory usage in histogram broken by datatypes

components/sync/base/data_type_histogram.h

Index: components/sync/base/data_type_histogram.h
diff --git a/components/sync/base/data_type_histogram.h b/components/sync/base/data_type_histogram.h
index 642c8848cc8dd3aebc42a3084d3ebf75eb3b9cba..09cc6f3e0c41c868e2749e4bc19b5d8e8f6ec7c8 100644
--- a/components/sync/base/data_type_histogram.h
+++ b/components/sync/base/data_type_histogram.h
@@ -11,12 +11,21 @@
 #include "base/time/time.h"
 #include "components/sync/base/model_type.h"
 
+// Prefix for histogram recording datatype's memory usage.
+extern const char kModelTypeMemoryHistogramPrefix[];
+
 // 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);
 
+// Converts memory size |value| into kilobytes and records it into |model_type|
+// related histogram with prefix |histogram_name_prefix|.
+void SyncRecordMemoryKbHistogram(const std::string& histogram_name_prefix,
+                                 syncer::ModelType model_type,
+                                 size_t 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)                                        \