Fix scheduled stream usage of asBroadcastStream
Fix scheduled stream usage of asBroadcastStream

This was causing tiemouts on the bots

BUG: 16023

R=ajohnsen@google.com, floitsch@google.com, nweiz@google.com

Review URL: https://codereview.chromium.org//137793004

git-svn-id: b90127a0f73590c96be848d3e4cb640efa9a7657@31820 260f80e4-7a28-3924-810f-c04153c831b5

dart-archive/scheduled_test,dart-lang/scheduled_test