Add a warning for the deprecation of content-initiated data URL navigations

third_party/WebKit/LayoutTests/fast/loader/stateobjects/pushstate-in-data-url-denied.html

 <script>
 if (window.testRunner) {
     testRunner.dumpAsText();
     testRunner.waitUntilDone();
 }
-window.onload = function() {
-    window.location = 'data:text/html,' +
-    '%3Cscript%3E' +
-    'try{' +
-        'history.pushState({},"","data:");' +
-        'document.write("FAIL data URL was manipula via pushState.");' +
-    '} catch(e) {' +
-        'document.write("PASS: data URLs cannot be manipulated via pushState.");' +
-    '}' +
-    'if (window.testRunner)' +
-        'testRunner.notifyDone();' +
-    '%3C/script%3E';
-}
 </script>
+<iframe src="data:text/html,
+  <script>
+  try{
+    history.pushState({}, '', 'data:');
+    alert('FAIL data URL was manipulated via pushState.');
+  } catch(e) {
+    alert('PASS: data URLs cannot be manipulated via pushState.');
+  }
+  if (window.testRunner)
+    testRunner.notifyDone();
+  </script>"></iframe>