Don't force layout for mouse event hit tests

LayoutTests/fast/events/script-tests/page-scaled-mouse-click.js

 description("This tests that page scaling does not affect mouse event pageX and pageY coordinates.");
 
 var html = document.documentElement;
 
 var div = document.createElement("div");
 div.style.width = "100px";
 div.style.height = "100px";
 div.style.backgroundColor = "blue";
 
 var eventLog = "";
@@ skipping 26 matching lines @@
 
 function testEvents(button, description, expectedString) {
     sendEvents(button);
     debug(description);
     shouldBeEqualToString("eventLog", expectedString);
     debug("");
     clearEventLog();
 }
 
 if (window.eventSender && window.internals) {
+    // Mouse events only work after an initial layout
+    document.body.offsetLeft;
+
     eventSender.mouseMoveTo(10, 10);
     // We are clicking in the same position on screen. As we scale or transform the page,
     // we expect the pageX and pageY event coordinates to change because different
     // parts of the document are under the mouse.
     testEvents(0, "Unscaled", "click(10, 10)");
 
     window.internals.setPageScaleFactor(0.5, 0, 0);
     testEvents(0, "setPageScale(0.5)", "click(20, 20)");
 }