temporarily disable OS X Chrome Sauce test since it's being flaky

e.g.:
Tested http://127.0.0.1:3000/js/tests/index.html
Environment: OS X 10.9::chrome
>> Timeout, waited for more than 300000 milliseconds

test-infra/sauce_browsers.yml

@@ -5,10 +5,11 @@
     browserName: "safari",
     platform: "OS X 10.9"
   },
-  {
-    browserName: "chrome",
-    platform: "OS X 10.9"
-  },
+  # FIXME: keeps timing out frequently for unknown reasons
+  # {
+  #   browserName: "chrome",
+  #   platform: "OS X 10.9"
+  # },
 
   {
     browserName: "firefox",