Lazily load extension API schemas

chrome/common/extensions/api/tts_engine.json

 // Copyright (c) 2012 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.
 
 [
   {
     "namespace": "ttsEngine",
-    "dependencies": [ "tts" ],
     "functions": [
       {
         "name": "sendTtsEvent",
         "nodoc": true,
         "type": "function",
         "description": "Routes a TTS event from a speech engine to a client.",
         "parameters": [
           {
             "type": "integer",
             "name": "requestId"
@@ skipping 76 matching lines @@
         ]
       },
       {
         "name": "onStop",
         "type": "function",
         "description": "Fired when a call is made to tts.stop and this extension may be in the middle of speaking. If an extension receives a call to onStop and speech is already stopped, it should do nothing (not raise an error)."
       }
     ]
   }
 ]