Adds extension APIs of events on changing volume.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "unprivileged": true,
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 485 matching lines @@
         "name": "onMenuClosed",
         "type": "function",
         "description": "Fired when a menu is closed.",
         "parameters": [
           {
             "$ref": "AccessibilityObject",
             "name": "menu",
             "description": "Information about the menu that was closed."
           }
         ]
+      },
+      {
+        "name": "onVolumeChanged",
+        "type": "function",
+        "description": "Fired when the volume is changed.",
+        "parameters": [
+          {
+            "$ref": "AccessibilityVolumeInfo",

[Zachary Kuznia, 2011/08/29 09:36:29]

I think you need to add AccessibilityVolumeInfo to the types section?

[yoshiki, 2011/08/29 11:50:43]

Done.

+            "name": "volume",
+            "description": "Information about the current volume level and the volume being muted."
+          }
+        ]
       }
     ]
   },
   {
     "namespace": "tts",
     "types": [
       {
         "id": "TtsEvent",
         "type": "object",
         "description": "An event from the TTS engine to communicate the status of an utterance.",
@@ skipping 7569 matching lines @@
                 "description": "A string result code. The value is non-empty on success only in tests.",
                 "optional": "true"
               }
             ]
           }
         ]
       }
     ]
   }
 ]