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

components/sync/syncable/directory.h

Index: components/sync/syncable/directory.h
diff --git a/components/sync/syncable/directory.h b/components/sync/syncable/directory.h
index 7e9ff063750dc009aca8864b0fea23ff88101ed4..5ac329648efedf03fb6891a4403db27166bf4768 100644
--- a/components/sync/syncable/directory.h
+++ b/components/sync/syncable/directory.h
@@ -292,6 +292,10 @@ class Directory {
   // Adds memory statistics to |pmd| for chrome://tracing.
   void OnMemoryDump(base::trace_event::ProcessMemoryDump* pmd);
 
+  // Estimates memory usage of entries and corresponding indices of type
+  // |model_type|.
+  size_t EstimateMemoryUsageByType(ModelType model_type);
+
   // Gets/Increments transaction version of a model type. Must be called when
   // holding kernel mutex.
   int64_t GetTransactionVersion(ModelType type) const;