Eliminate globalFlag usage from http security layout tests.

LayoutTests/http/tests/security/cross-frame-access-get-custom-property-cached.html

Index: LayoutTests/http/tests/security/cross-frame-access-get-custom-property-cached.html
diff --git a/LayoutTests/http/tests/security/cross-frame-access-get-custom-property-cached.html b/LayoutTests/http/tests/security/cross-frame-access-get-custom-property-cached.html
index f6d6c5a422e5ca9b6b540908d16ac964f920507d..85b95ac8c1e2cff331e8935eabb83b928b16b2f8 100644
--- a/LayoutTests/http/tests/security/cross-frame-access-get-custom-property-cached.html
+++ b/LayoutTests/http/tests/security/cross-frame-access-get-custom-property-cached.html
@@ -9,25 +9,12 @@
                 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();
+                if (window.testRunner)
+                    testRunner.notifyDone();
+            });
         }
 
         function customPropertyAccessThrowsException(o)