Extension Storage API: expose storage quota information to extensions, via:

chrome/renderer/resources/extensions/storage_custom_bindings.js

 // 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.
 
 // Custom bindings for the storage API.
 
 (function() {
 
 native function GetChromeHidden();
 
 var chromeHidden = GetChromeHidden();
 
-chromeHidden.registerCustomType('StorageNamespace',
-    function(typesAPI) {
+chromeHidden.registerCustomType('StorageArea', function(typesAPI) {
   var sendRequest = typesAPI.sendRequest;
 
   function extendSchema(schema) {
     var extendedSchema = schema.slice();
     extendedSchema.unshift({'type': 'string'});
     return extendedSchema;
   }
 
-  function StorageNamespace(namespace, schema) {
+  function StorageArea(namespace, schema) {
     // Binds an API function for a namespace to its browser-side call, e.g.
     // storage.sync.get('foo') -> (binds to) ->
     // storage.get('sync', 'foo').
     //
     // TODO(kalman): Put as a method on CustomBindingsObject and re-use (or
     // even generate) for other APIs that need to do this. Same for other
     // callers of registerCustomType().
     function bindApiFunction(functionName) {
       this[functionName] = function() {
         var schema = this.parameters[functionName];
         chromeHidden.validate(arguments, schema);
         return sendRequest(
             'storage.' + functionName,
             [namespace].concat(Array.prototype.slice.call(arguments)),
             extendSchema(schema));
       };
     }
-    ['get', 'set', 'remove', 'clear'].forEach(bindApiFunction.bind(this));
+    var apiFunctions = ['get', 'set', 'remove', 'clear', 'getBytesInUse'];
+    apiFunctions.forEach(bindApiFunction.bind(this));
   }
 
-  return StorageNamespace;
+  return StorageArea;
 });
 
 })();