[Sync] Implement MemoryDumpProvider.

components/sync/syncable/directory_backing_store.cc

Index: components/sync/syncable/directory_backing_store.cc
diff --git a/components/sync/syncable/directory_backing_store.cc b/components/sync/syncable/directory_backing_store.cc
index 134e674a3065b3b220b48201cf889dd4dd90c3a9..e4306177731f1b8b001a921b50b77615d5bd37b5 100644
--- a/components/sync/syncable/directory_backing_store.cc
+++ b/components/sync/syncable/directory_backing_store.cc
@@ -1718,6 +1718,11 @@ bool DirectoryBackingStore::GetDatabasePageSize(int* page_size) {
   return true;
 }
 
+bool DirectoryBackingStore::ReportMemoryUsage(
+    base::trace_event::MemoryAllocatorDump* mad) {
+  return db_ && db_->ReportMemoryUsage(mad);
+}
+
 bool DirectoryBackingStore::UpdatePageSizeIfNecessary() {
   int page_size;
   if (!GetDatabasePageSize(&page_size))