[whatwg] FileList usage

[Erik Arvidsson]

Now that we are removing usages of DOMStringList it is also tempting
to look at other list interfaces that only have item/length. Searching
through the WebKit IDL files the following are dumb:

ClientRectList
CSSRuleList
CSSValueList
EntryArray
EntryArraySync
FileList
GamepadList
MediaStreamList
MediaStreamTrackList
SpeechInputResultList
SQLResultSetRowList
StyleSheetList
WebKitAnimationList (WebKit only)

I believe that all of these could be removed in favor for Array but I
can understand that there might be some concerns here due to backward
compatibility. Some of these are very new and should be safe to just
change (media, file system, gamepad, speech, wk animation)

erik