Round coordinate passed to pointerMove.

Differential Revision: https://phabricator.services.mozilla.com/D40541

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1541573
gecko-commit: ba13ac52e22a0c8fce78312520418dd2bae349ac
gecko-integration-branch: autoland
gecko-reviewers: smaug

Author: upsuper

pointerlock/movementX_Y_basic.html

@@ -128,8 +128,8 @@ <h2>Manual Test Steps:</h2>
         }
 
         function run_test() {
-            x = window.innerWidth / 2;
-            y = window.innerHeight / 2;
+            x = Math.round(window.innerWidth / 2);
+            y = Math.round(window.innerHeight / 2);
             var actions = new test_driver.Actions();
             actions.pointerMove(x, y)
               .pointerDown()