Implement throttling behavior for LocalStorage mojo messages.

content/common/leveldb_wrapper.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module content.mojom;
 
 import "components/leveldb/public/interfaces/leveldb.mojom";
 
 // Gives information about changes to a LevelDB database.
 // Note that observer methods are called before the callbacks for the
@@ skipping 37 matching lines @@
   // Removes all the entries.
   DeleteAll(string source) => (bool success);
 
   // Returns the value of the |key|.
   Get(array<uint8> key) => (bool success, array<uint8> value);
 
   // Only used with small databases. Returns all key/value pairs.
   [Sync]
   GetAll(associated LevelDBWrapperGetAllCallback complete_callback)
     => (leveldb.mojom.DatabaseError status, array<KeyValue> data);
+
+  [Sync] FlushPipe() => ();
 };