Change these tests to actually trigger the execCommand from the iframe context.

chrome/test/data/extensions/api_test/clipboard/extension/test.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.
 
 // Clipboard permission test for Chrome.
 // browser_tests.exe --gtest_filter=ClipboardApiTest.Extension
 
 chrome.test.runTests([
   function domCopy() {
     if (document.execCommand('copy'))
       chrome.test.succeed();
     else
       chrome.test.fail('execCommand("copy") failed');
   },
   function domPaste() {
     if (document.execCommand('paste'))
       chrome.test.succeed();
     else
       chrome.test.fail('execCommand("paste") failed');
   },
   function copyInIframe() {
     var ifr = document.createElement('iframe');
     document.body.appendChild(ifr);
-    if (ifr.contentDocument.execCommand('copy'))
-      chrome.test.succeed();
-    else
-      chrome.test.fail('execCommand("copy") failed in iframe');
+    window.command = 'copy';
+    ifr.contentDocument.write('<script src="iframe.js"></script>');
   },
   function pasteInIframe() {
     var ifr = document.createElement('iframe');
     document.body.appendChild(ifr);
-    if (ifr.contentDocument.execCommand('paste'))
-      chrome.test.succeed();
-    else
-      chrome.test.fail('execCommand("paste") failed in iframe');
+    window.command = 'paste';
+    ifr.contentDocument.write('<script src="iframe.js"></script>');
   }
 ]);
 
+
+function testDone(result) {
+  if (result)
+    chrome.test.succeed();
+  else
+    chrome.test.fail();
+}