Add test case for mouseleave events within window bounds

LayoutTests/fast/events/event-sender-mouseleave.html

+<!DOCTYPE html>
+<style>
+#testBox {
+    background: blue;
+    top: 100px;
+    left: 100px;
+    width: 100px;
+    height: 100px;
+    position: absolute;
+}
+</style>
+<div id="testBox">
+</div>
+<p id="description">
+</p>
+<script src="../../resources/js-test.js"></script>
+<script>
+    window.jsTestIsAsync = true;
+
+    description('Test that a mouse leave event is triggered when the OS tells us the mouse has left without changing position.');
+    var hasMouseLeave = false;
+    var hasMouseOut = false;
+    var box = document.getElementById('testBox');
+    var lastMouseX = 0;
+    var lastMouseY = 0;
+    box.addEventListener('mouseleave', function (e) {
+        hasMouseLeave = true;
+        lastMouseX = e.clientX;
+        lastMouseY = e.clientY;
+    });
+    box.addEventListener('mouseout', function () {
+        hasMouseOut = true;
+    });
+    if (window.testRunner) {
+        eventSender.mouseMoveTo(1, 1);
+        eventSender.mouseMoveTo(box.offsetLeft + 10, box.offsetTop + 10);
+        eventSender.mouseLeave();
+        shouldBeTrue('hasMouseLeave');
+        shouldBeTrue('hasMouseOut');
+        shouldBe('box.offsetLeft + 10', 'lastMouseX');
+        shouldBe('box.offsetTop + 10', 'lastMouseY');
+        finishJSTest();
+    }
+</script>