[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 07867bb76398edac24d937535f53cffd7c5d250d..bc73993513760ed1c4ea80d94fe493e3e991978f 100644
--- a/components/sync/syncable/directory_backing_store.cc
+++ b/components/sync/syncable/directory_backing_store.cc
@@ -1717,6 +1717,11 @@ 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))