Do not allow streams to send events during state-change callbacks.

Change Stream callbacks.
    
During a stat-change callback, events can't be fired. Any events added will be delayed.
    
When both the subscription state and the pause state has changed in a single operation, only the subscription state change callback is called.
    
After calling _close on a Stream (close on a StreamController/scheduling a Done event), the pause-state change callback will no longer be called. All necessary pause handling will be done internally in the Stream, since the stream controller can't add any new events anyway.

Committed: https://code.google.com/p/dart/source/detail?r=18748

[Lasse Reichstein Nielsen, 2013-02-20 12:25:23]

Will need to run more tests.

[Anders Johnsen, 2013-02-20 12:42:02]

STV!!!

https://codereview.chromium.org/12319010/diff/2001/sdk/lib/async/stream_impl....
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/12319010/diff/2001/sdk/lib/async/stream_impl....
sdk/lib/async/stream_impl.dart:234: 
Extra space.

https://codereview.chromium.org/12319010/diff/2001/sdk/lib/async/stream_impl....
sdk/lib/async/stream_impl.dart:474: // A single-stream is considered paused when
it has no subscriber.
Comment.

https://codereview.chromium.org/12319010/diff/2001/tests/lib/async/slow_consu...
File tests/lib/async/slow_consumer_test.dart (left):

https://codereview.chromium.org/12319010/diff/2001/tests/lib/async/slow_consu...
tests/lib/async/slow_consumer_test.dart:58: 
Reintroduce this space.

[Lasse Reichstein Nielsen, 2013-02-20 12:45:55]

Committed patchset #2 manually as r18748 (presubmit successful).