Add tests to make sure copy/paste in an about:blank iframe in a hosted app works.

chrome/test/data/extensions/api_test/clipboard/extension/test.js

Index: chrome/test/data/extensions/api_test/clipboard/extension/test.js
diff --git a/chrome/test/data/extensions/api_test/clipboard/extension/test.js b/chrome/test/data/extensions/api_test/clipboard/extension/test.js
index 8432db7e2ab10bcc7c07459a16fd54de9b085463..4206d24e5b79453cdcbee5bb898e4845eb747340 100644
--- a/chrome/test/data/extensions/api_test/clipboard/extension/test.js
+++ b/chrome/test/data/extensions/api_test/clipboard/extension/test.js
@@ -17,6 +17,22 @@ chrome.test.runTests([
       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');
+  },
+  function pasteInIframe() {
+    var ifr = document.createElement('iframe');
+    document.body.appendChild(ifr);
+    if (ifr.contentDocument.execCommand('paste'))

[not at google - send to devlin, 2014/08/22 14:03:13]

Ok - I was being a bit silly here. I *would* expect this to work because the
execCommand call is still coming from the same context (this one).

The actual way to trigger an execCommand from a different context would be:

ifr.contentDocument.write('<script>execCommand("copy")</script>')

+      chrome.test.succeed();
+    else
+      chrome.test.fail('execCommand("paste") failed in iframe');
   }
 ]);