Tabs API is usable without tabs permission.

chrome/test/data/extensions/api_test/active_tab/background.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.
 
 var theOnlyTestDone = null;
 
 function inject(callback) {
   chrome.tabs.executeScript({ code: "true" }, callback);
 }
 
 chrome.browserAction.onClicked.addListener(function() {
   inject(function() {
     chrome.test.assertNoLastError();
     chrome.test.notifyPass();
   });
 });
 
 chrome.webNavigation.onCompleted.addListener(function(details) {
   inject(function() {
-    chrome.test.assertLastError("Access to extension API denied.");
+    chrome.test.assertLastError('Cannot access contents of url "' +
+        details.url +
+        '". Extension manifest must request permission to access this host.');
     if (details.url.indexOf("final_page") >= 0)
       theOnlyTestDone();
     else
       chrome.test.notifyPass();
   });
 });
 
 chrome.test.runTests([
   function theOnlyTest() {
     // This will keep the test alive until the final callback is run.
     theOnlyTestDone = chrome.test.callbackAdded();
   }
 ]);