[Sync] Implement MemoryDumpProvider.

components/sync/syncable/directory_backing_store.h

Index: components/sync/syncable/directory_backing_store.h
diff --git a/components/sync/syncable/directory_backing_store.h b/components/sync/syncable/directory_backing_store.h
index 1c0cdde786df6eb4f8d22ae5e2aecf5aae70a3fe..002f530499c82d1edadce644389f84178eb75166 100644
--- a/components/sync/syncable/directory_backing_store.h
+++ b/components/sync/syncable/directory_backing_store.h
@@ -20,6 +20,12 @@
 #include "sql/connection.h"
 #include "sql/statement.h"
 
+namespace base {
+namespace trace_event {
+class MemoryAllocatorDump;
+}
+}
+
 namespace sync_pb {
 class EntitySpecifics;
 }
@@ -100,6 +106,8 @@ class DirectoryBackingStore : public base::NonThreadSafe {
   // Returns true on success, false on error.
   bool GetDatabasePageSize(int* page_size);
 
+  bool ReportMemoryUsage(base::trace_event::MemoryAllocatorDump* mad);
+
  protected:
   // For test classes.
   DirectoryBackingStore(const std::string& dir_name,