Avoid sending needless data between isolates in "pub serve" and "pub build"

Avoid sending needless data between isolates in "pub serve" and "pub build"

Previously when passing barback assets between isolates, pub would eagerly send
the entire contents of the asset. Now it waits to do so until some code actually
subscribes to the asset's data stream.

BUG=14430
R=rnystrom@google.com

Committed: https://code.google.com/p/dart/source/detail?r=29408

[Bob Nystrom, 2013-10-25 23:44:18]

LGTM!

[nweiz, 2013-10-28 23:39:49]

I just merged this with the recent isolate changes and there was rather a lot of
churn. PTAL.

[Bob Nystrom, 2013-10-28 23:52:49]

Couple of questions, but LGTM assuming I have the right answers.

https://codereview.chromium.org/43143002/diff/50001/sdk/lib/_internal/pub/lib...
File sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart (right):

https://codereview.chromium.org/43143002/diff/50001/sdk/lib/_internal/pub/lib...
sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart:603: var
receivePort = new ReceivePort();
This needs to be explicitly closed now, right?

Does this just rely on the stream returned by this being closed?

[nweiz, 2013-10-29 00:15:55]

https://codereview.chromium.org/43143002/diff/50001/sdk/lib/_internal/pub/lib...
File sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart (right):

https://codereview.chromium.org/43143002/diff/50001/sdk/lib/_internal/pub/lib...
sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart:603: var
receivePort = new ReceivePort();
On 2013/10/28 23:52:49, Bob Nystrom wrote:
> This needs to be explicitly closed now, right?
> 
> Does this just rely on the stream returned by this being closed?

Once a "done" event is received, the subscription on the receivePort will be
closed, which will close the port itself. Alternately if a user closes the
returned stream early the port will be closed as well.

[nweiz, 2013-10-29 00:18:27]

Committed patchset #2 manually as r29408 (presubmit successful).