[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..51d9c4e749c98288da3c7f27b9239ca66dc86587 100644
--- a/components/sync/base/data_type_histogram.h
+++ b/components/sync/base/data_type_histogram.h
@@ -17,6 +17,12 @@
 // So different DataTypes play the role of different buckets in this histogram.
 void SyncRecordDatatypeBin(const std::string& name, int sample, int value);
 
+// Records memory size |value| in kilobytes 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)                                        \