Bug 753323 - Wait until actually in fullscreen before starting screenClientXPConst pointer lock test. r=orange-fix

dom/tests/mochitest/pointerlock/file_screenClientXYConst.html

@@ -85,15 +85,25 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=633602
         }
       }, false);
 
-      document.addEventListener("mozfullscreenchange", function() {
+      function fullscreenchange() {
+        var screenX = window.screenX;
+        var screenY = window.screenY;
         if (document.mozFullScreenElement === div) {
+          if (screenX != 0 || screenY != 0) {
+            todo(screenX == 0 && screenY == 0,
+              "We should only receive fullscreenchange once we've finished fullscreen transition " +
+              "window.screenX=" + screenX + " window.screenY=" + screenY);
+            setTimeout(fullscreenchange, 250);
+            return;
+          }
           div.addEventListener("mousemove", moveUnlocked, false);
           synthesizeMouseAtCenter(div, { type: "mousemove" }, window);
         } else {
           runTests();
           SimpleTest.finish();
         }
-      }, false);
+      }
+      document.addEventListener("mozfullscreenchange", fullscreenchange, false);
 
       function start() {
         div = document.getElementById("div");