Defer updateCompositingRequirementsState until the compositing update

LayoutTests/compositing/overflow/overflow-scroll.html

Index: LayoutTests/compositing/overflow/overflow-scroll.html
diff --git a/LayoutTests/compositing/overflow/overflow-scroll.html b/LayoutTests/compositing/overflow/overflow-scroll.html
index aa10dc5e3a8c6ea8aa82980a25157690fe6d6121..742e1faa1846ac207fbc8a3764b6cfc659f90eb2 100644
--- a/LayoutTests/compositing/overflow/overflow-scroll.html
+++ b/LayoutTests/compositing/overflow/overflow-scroll.html
@@ -35,8 +35,12 @@
         scrollables[i].scrollTop = 50;
       }
 
-      if (window.testRunner)
-        testRunner.notifyDone();
+      requestAnimationFrame(function() {
+        setTimeout(function() {
+          if (window.testRunner)
+            testRunner.notifyDone();
+        });
+      });
     }
 
     window.addEventListener('load', doTest, false);