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

chrome/renderer/resources/extensions/storage_custom_bindings.js

Index: chrome/renderer/resources/extensions/storage_custom_bindings.js
diff --git a/chrome/renderer/resources/extensions/storage_custom_bindings.js b/chrome/renderer/resources/extensions/storage_custom_bindings.js
index cd58774f5be0757b63838b22a0d9558d59bdeb62..1d358c29b7f01d967aa458941c22656072ac690c 100644
--- a/chrome/renderer/resources/extensions/storage_custom_bindings.js
+++ b/chrome/renderer/resources/extensions/storage_custom_bindings.js
@@ -10,8 +10,7 @@ native function GetChromeHidden();
 
 var chromeHidden = GetChromeHidden();
 
-chromeHidden.registerCustomType('StorageNamespace',
-    function(typesAPI) {
+chromeHidden.registerCustomType('StorageArea', function(typesAPI) {
   var sendRequest = typesAPI.sendRequest;
 
   function extendSchema(schema) {
@@ -20,7 +19,7 @@ chromeHidden.registerCustomType('StorageNamespace',
     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').
@@ -38,10 +37,11 @@ chromeHidden.registerCustomType('StorageNamespace',
             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;
 });
 
 })();