Make LevelDBObserver an associated interface to LevelDBWrapper.

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 12 matching lines @@
 };
 
 struct KeyValue {
   array<uint8> key;
   array<uint8> value;
 };
 
 // A wrapper around leveldb that supports giving notifications when values
 // change.
 interface LevelDBWrapper {
+  AddObserver(associated LevelDBObserver observer);
+
   // Sets the database entry for |key| to |value|. Returns OK on success.
   Put(array<uint8> key, array<uint8> value, string source) => (bool success);
 
   // Remove the database entry (if any) for |key|.  Returns OK on success, and a
   // non-OK status on error.  It is not an error if |key| did not exist in the
   // database.
   Delete(array<uint8> key, string source) => (bool success);
 
   // 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(string source)
     => (leveldb.mojom.DatabaseError status, array<KeyValue> data);
 };