Bug 1177018 - Disable smooth scrolling in the APZ layerization test. r=kats

--HG--
extra : rebase_source : ee705290c57e3122bac17af9ee70aa6c4e76c285
extra : source : d5f9fb06ee8c344f35fcf9fd86b5f654862ec1e8

gfx/layers/apz/test/test_layerization.html

@@ -150,8 +150,14 @@ function startTest() {
 }
 
 SimpleTest.waitForExplicitFinish();
-SimpleTest.waitForFocus(startTest, window);
 
+// Disable smooth scrolling, because it results in long-running scroll
+// animations that can result in a 'scroll' event triggered by an earlier
+// wheel event as corresponding to a later wheel event.
+SpecialPowers.pushPrefEnv({"set": [["general.smoothScroll", false]]},
+                          function() {
+                            SimpleTest.waitForFocus(startTest, window);
+                          });
 </script>
 </pre>
 </body>