Don't force layout for mouse event hit tests

LayoutTests/fast/forms/input-text-self-emptying-click.html

Index: LayoutTests/fast/forms/input-text-self-emptying-click.html
diff --git a/LayoutTests/fast/forms/input-text-self-emptying-click.html b/LayoutTests/fast/forms/input-text-self-emptying-click.html
index eb8b54948c30c832afb91c602c9ecd5a238635b8..0ab3f873d57799ce34cc9740bdb0d8de8c45cef4 100644
--- a/LayoutTests/fast/forms/input-text-self-emptying-click.html
+++ b/LayoutTests/fast/forms/input-text-self-emptying-click.html
@@ -2,6 +2,8 @@
 <p>Tests clicking on an input element that has a value that self-destructs. If the test succeeds, there should be a blinking caret in the text field.</p>
 <script>
 if (window.eventSender) {
+    // Mouse events only work after an initial layout
+    document.body.offsetLeft;
     eventSender.mouseMoveTo(15, 15);
     eventSender.mouseDown();
     eventSender.mouseUp();