Oilpan: add transition types to track interface objects.

Source/core/html/track/vtt/VTTRegion.idl

 /*
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 [
     Constructor,
-    RuntimeEnabled=WebVTTRegions
+    RuntimeEnabled=WebVTTRegions,
+    WillBeGarbageCollected,
 ] interface VTTRegion {
     readonly attribute TextTrack track;
 
     attribute DOMString id;
     [RaisesException=Setter] attribute double width;
     [RaisesException=Setter] attribute long height;
     [RaisesException=Setter] attribute double regionAnchorX;
     [RaisesException=Setter] attribute double regionAnchorY;
     [RaisesException=Setter] attribute double viewportAnchorX;
     [RaisesException=Setter] attribute double viewportAnchorY;
     [RaisesException=Setter] attribute DOMString scroll;
 };