Bug 1264182: Hide URL.createObjectURL from ServiceWorker r=mrbkap,asuth

The appropriate lifetime for URLs created with URL.createObjectURL turned
out to be tricky to define, so it was decided to hide it from service
workers altogether. (w3c/ServiceWorker#688)

This commit implements this change and adds a web platform test to verify it.
It also exposes the MediaSource variant of URL.createObjectURL in DedicatedWorker
and SharedWorker contexts in order to comply with the WebIDL spec (see
w3c/media-source#168 (comment)).

Differential Revision: https://phabricator.services.mozilla.com/D2728

UltraBlame original commit: 40d4999db3191bca0aeb75a50b37537ad78102ed

dom/webidl/URL.webidl

@@ -278,6 +278,15 @@ toJSON
 ;
 }
 ;
+[
+Exposed
+=
+(
+Window
+DedicatedWorker
+SharedWorker
+)
+]
 partial
 interface
 URL
@@ -316,8 +325,6 @@ DOMString
 url
 )
 ;
-}
-;
 /
 /
 https
@@ -351,10 +358,6 @@ media
 source
 .
 html
-partial
-interface
-URL
-{
 [
 Throws
 ]

testing/web-platform/tests/service-workers/service-worker/resources/interfaces-worker.sub.js

@@ -803,3 +803,31 @@ exposed
 '
 )
 ;
+test
+(
+(
+)
+=
+>
+{
+assert_false
+(
+'
+createObjectURL
+'
+in
+self
+.
+URL
+)
+;
+}
+'
+URL
+.
+createObjectURL
+is
+not
+exposed
+'
+)