Add SecureContext to ImageTrack, ImageTrackList

These aren't constructible by the page, so they should have the
same SecureContext annotation that ImageDecoder does.

Author: dalecurtis

index.src.html

@@ -6032,7 +6032,7 @@
 ----------------------------------------------------
 <pre class='idl'>
 <xmp>
-[Exposed=(Window,DedicatedWorker)]
+[Exposed=(Window,DedicatedWorker), SecureContext]
 interface ImageTrackList {
   getter ImageTrack (unsigned long index);
 
@@ -6083,7 +6083,7 @@
 --------------------------------------------
 <pre class='idl'>
 <xmp>
-[Exposed=(Window,DedicatedWorker)]
+[Exposed=(Window,DedicatedWorker), SecureContext]
 interface ImageTrack {
   readonly attribute boolean animated;
   readonly attribute unsigned long frameCount;