Bug 1523562 [wpt PR 15034] - Update interfaces/mediastream-recording.idl, a=testonly

Automatic update from web-platform-tests
Update interfaces/mediastream-recording.idl (#15034)

Source: https://github.com/tidoust/reffy-reports/blob/cd28628/whatwg/idl/mediastream-recording.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/483763432
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wpt-commits: 4394109df7c7ac88a67d33873cd1653892a9fe20
wpt-pr: 15034

testing/web-platform/tests/interfaces/mediastream-recording.idl

@@ -18,7 +18,7 @@ interface MediaRecorder : EventTarget {
   readonly attribute unsigned long videoBitsPerSecond;
   readonly attribute unsigned long audioBitsPerSecond;
 
-  void start(optional long timeslice);
+  void start(optional unsigned long timeslice);
   void stop();
   void pause();
   void resume();