Bug 1452926 - add easing back to videocontrol control animations, r=timdream

MozReview-Commit-ID: w8rdA1uk5H

--HG--
extra : rebase_source : 4aab405627ba2ad6fb276c8d522c1d59891d25f2

toolkit/content/widgets/videocontrols.xml

@@ -1102,6 +1102,7 @@
             { transform: "scale(1)", opacity: 0.55 }
           ],
           options: {
+            easing: "ease",
             duration: 400
           }
         },
@@ -1111,6 +1112,7 @@
             { opacity: 1 }
           ],
           options: {
+            easing: "ease",
             duration: 200
           }
         },