Eliminate globalFlag usage from http security layout tests.

LayoutTests/http/tests/security/dataURL/xss-DENIED-to-data-url-in-foreign-domain-subframe.html

Index: LayoutTests/http/tests/security/dataURL/xss-DENIED-to-data-url-in-foreign-domain-subframe.html
diff --git a/LayoutTests/http/tests/security/dataURL/xss-DENIED-to-data-url-in-foreign-domain-subframe.html b/LayoutTests/http/tests/security/dataURL/xss-DENIED-to-data-url-in-foreign-domain-subframe.html
index 0d6a9bea6687fad9d1c8c40b9bfe90b5a62f7c9b..53dfb4cee8442b824affe33ba5e3d1e8eb8f9f83 100644
--- a/LayoutTests/http/tests/security/dataURL/xss-DENIED-to-data-url-in-foreign-domain-subframe.html
+++ b/LayoutTests/http/tests/security/dataURL/xss-DENIED-to-data-url-in-foreign-domain-subframe.html
@@ -10,25 +10,11 @@
                 testRunner.waitUntilDone();
             }
 
-            if (window.testRunner) {
-                setTimeout(pollForTest, 1);
-            } else {
-                log("To run the test, click the button below when the opened window finishes loading.");
-                var button = document.createElement("button");
-                button.appendChild(document.createTextNode("Run Test"));
-                button.onclick = runTest;
-                document.body.appendChild(button);
-            }
-        }
-
-        pollForTest = function()
-        {
-            if (!testRunner.globalFlag) {
-                setTimeout(pollForTest, 1);
-                return;
-            }
-            runTest();
-            testRunner.notifyDone();
+            window.addEventListener('message', function ()
+            {
+                runTest();
+                testRunner.notifyDone();
+            });
         }
 
         runTest = function()