[css-animations-2][css-transitions-2] Add [Exposed=Window] annotation to CSSAnimation and CSSTransition interfaces

For whatwg/webidl#365.

Author: birtles

css-animations-2/Overview.bs

@@ -539,6 +539,7 @@ the {{AnimationEvent}}.
 ## The CSSAnimation interface ## {#the-CSSAnimation-interface}
 
 <pre class="idl">
+[Exposed=Window]
 interface CSSAnimation : Animation {
   readonly attribute CSSOMString animationName;
 };

css-transitions-2/Overview.bs

@@ -340,6 +340,7 @@ the {{TransitionEvent}}.
 ## The CSSTransition interface ## {#the-CSSTransition-interface}
 
 <pre class="idl">
+[Exposed=Window]
 interface CSSTransition : Animation {
   readonly attribute CSSOMString transitionProperty;
 };