Update layout tests to work when smooth scrolling is enabled by default

third_party/WebKit/LayoutTests/fast/scrolling/absolute-position-behind-scrollbar.html

Index: third_party/WebKit/LayoutTests/fast/scrolling/absolute-position-behind-scrollbar.html
diff --git a/third_party/WebKit/LayoutTests/fast/scrolling/absolute-position-behind-scrollbar.html b/third_party/WebKit/LayoutTests/fast/scrolling/absolute-position-behind-scrollbar.html
index 9f1679037db9d90d64fee3f8f1811d7643a7712b..e45a56054cc8bef6d92da4f290b3212cb0250e1e 100644
--- a/third_party/WebKit/LayoutTests/fast/scrolling/absolute-position-behind-scrollbar.html
+++ b/third_party/WebKit/LayoutTests/fast/scrolling/absolute-position-behind-scrollbar.html
@@ -13,11 +13,14 @@
 Tests that the scrollbar can be clicked even when it clips absolute-positioned content.
 <div id="a"></div>
 <script>
+window.jsTestIsAsync = true;
 
-eventSender.mouseMoveTo(790, 500);
-eventSender.mouseDown();
-eventSender.mouseUp();
-
-shouldBeTrue(String(scrollY > 0));
+function runTest() {
+  eventSender.mouseMoveTo(790, 500);
+  eventSender.mouseDown();
+  eventSender.mouseUp();
+  shouldBecomeEqual('scrollY > 0', 'true', finishJSTest);
+}
 
+onload = runTest;
 </script>