Initialize content scripts the same way extension scripts are.

chrome/renderer/resources/renderer_extension_bindings.js

 // Copyright (c) 2011 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.
 
 // This script contains unprivileged javascript APIs related to chrome
 // extensions.  It is loaded by any extension-related context, such as content
 // scripts or toolstrips.
 // See user_script_slave.cc for script that is loaded by content scripts only.
 // TODO(mpcomplete): we also load this in regular web pages, but don't need to.
 
@@ skipping 155 matching lines @@
 
     PortRelease(portId);
     chromeHidden.onUnload.removeListener(portReleasers[portId]);
 
     delete ports[portId];
     delete portReleasers[portId];
   };
 
   // This function is called on context initialization for both content scripts
   // and extension contexts.
-  chrome.initExtension = function(extensionId, warnOnPrivilegedApiAccess,
-                                  inIncognitoContext) {
-    delete chrome.initExtension;
+  chromeHidden.onLoad.addListener(function(extensionId, isExtensionProcess,
+                                           inIncognitoContext) {
     chromeHidden.extensionId = extensionId;
 
     chrome.extension = chrome.extension || {};
     chrome.self = chrome.extension;
 
     chrome.extension.inIncognitoTab = inIncognitoContext;  // deprecated
     chrome.extension.inIncognitoContext = inIncognitoContext;
 
     // Events for when a message channel is opened to our extension.
     chrome.extension.onConnect = new chrome.Event();
@@ skipping 63 matching lines @@
       if (!path.length || path[0] != "/")
         path = "/" + path;
       return "chrome-extension://" + extensionId + path;
     };
 
     chrome.i18n = chrome.i18n || {};
     chrome.i18n.getMessage = function(message_name, placeholders) {
       return GetL10nMessage(message_name, placeholders, extensionId);
     };
 
-    if (warnOnPrivilegedApiAccess) {
+    if (!isExtensionProcess)
       setupApiStubs();
-    }
-  };
+  });
 
   var notSupportedSuffix = " is not supported in content scripts. " +
       "See the content scripts documentation for more details.";
 
   // Setup to throw an error message when trying to access |name| on the chrome
   // object. The |name| can be a dot-separated path.
   function createStub(name) {
     var module = chrome;
     var parts = name.split(".");
     for (var i = 0; i < parts.length - 1; i++) {
@@ skipping 77 matching lines @@
       "extension.onRequestExternal",
       "extension.setUpdateUrlData",
       "i18n.getAcceptLanguages"
     ];
     for (var i = 0; i < privileged.length; i++) {
       createStub(privileged[i]);
     }
   }
 
 })();