Use sequence<T> instead of T[] where possible and document exceptions

third_party/WebKit/Source/modules/mediasource/TrackDefault.idl

Index: third_party/WebKit/Source/modules/mediasource/TrackDefault.idl
diff --git a/third_party/WebKit/Source/modules/mediasource/TrackDefault.idl b/third_party/WebKit/Source/modules/mediasource/TrackDefault.idl
index 1e4854df71fa908c1bc5083c1880479ff588e88d..119c15fdeda670995135533fd19683ceddcfb1ed 100644
--- a/third_party/WebKit/Source/modules/mediasource/TrackDefault.idl
+++ b/third_party/WebKit/Source/modules/mediasource/TrackDefault.idl
@@ -16,5 +16,6 @@ enum TrackDefaultType { "audio", "video", "text" };
     readonly attribute DOMString byteStreamTrackID;
     readonly attribute DOMString language;
     readonly attribute DOMString label;
+    // TODO(wolenetz): |kinds| should be FrozenArray<DOMString>.

[wolenetz, 2016/10/03 20:53:03]

LGTM % reference https://crbug.com/619665 here please. Note, v1 MSE spec dropped
this feature, but it'll likely come back in incubation. Right before it was
dropped, this attribute was changed to sequence<DOMString> getKinds() accessor.
That crbug tracks updating this object to that latter change.

[foolip, 2016/10/04 10:02:20]

Referencing https://crbug.com/619665 and
https://github.com/w3c/media-source/issues/91.

FWIW, if the constructor is the only way to create an object like this, I think
that a [SameObject] FrozenArray<DOMString> would have been more in line with
other APIs like https://notifications.spec.whatwg.org/#api

     readonly attribute DOMString[] kinds;
 };