Clean up how we handle themes in the extensions system and management API....

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 4247 matching lines @@
             "type": "string"
           },
           "enabled": {
             "description": "Whether it is currently enabled or disabled.",
             "type": "boolean"
           },
           "isApp": {
             "description": "True if this is an app.",
             "type": "boolean"
           },
+          "isTheme": {
+            "description": "True if this is a theme.",
+            "type": "boolean"
+          },
           "appLaunchUrl": {
             "description": "The launch url (only present for apps).",
             "type": "string",
             "optional": true
           },
           "optionsUrl": {
             "description": "The url for the item's options page, if it has one.",
             "type": "string"
           },
           "icons": {
@@ skipping 141 matching lines @@
         ]
       },
       {
         "name": "onEnabled",
         "description": "Fired when an app or extension has been enabled.",
         "type": "function",
         "parameters": [{"name": "info", "$ref":"ExtensionInfo"}]
       },
       {
         "name": "onDisabled",
-        "description": "Fired when an app or extension has been disabled",
+        "description": "Fired when an app or extension has been disabled.",
         "type": "function",
         "parameters": [{"name": "info", "$ref":"ExtensionInfo"}]
       }
     ]
   },
 
   {
     "namespace":"webstorePrivate",
     "nodoc": "true",
     "functions": [
@@ skipping 113 matching lines @@
                   "token": { "type": "string", "optional": true }
                 }
               }
             ]
           }
         ]
       }
     ]
   }
 ]