Fix use of Process API in pub.

Fix use of Process API in pub.

This is subtle, but you have to wait for the process to be started
before you can write to its stdin stream. You can register event
handlers on the output streams if you want but you have to wait with
writing to stdin.

R=sgjesse@google.com,nweiz@google.com,rnystrom@google.com
BUG=dartbug.com/5065

Committed: https://code.google.com/p/dart/source/detail?r=12559

[Søren Gjesse, 2012-09-19 13:34:03]

LGTM!

[Bob Nystrom, 2012-09-19 16:12:26]

LGTM! Thanks for tracking this down!

[nweiz, 2012-09-19 18:09:45]

https://codereview.chromium.org/10947031/diff/1/utils/pub/io.dart
File utils/pub/io.dart (right):

https://codereview.chromium.org/10947031/diff/1/utils/pub/io.dart#newcode594
utils/pub/io.dart:594: process.onError = completer.completeException;
What happens if "tar" isn't found? Will onStart fire, then onError? If not, the
completer will never fire.

[Mads Ager (google), 2012-09-20 06:16:26]

https://codereview.chromium.org/10947031/diff/1/utils/pub/io.dart
File utils/pub/io.dart (right):

https://codereview.chromium.org/10947031/diff/1/utils/pub/io.dart#newcode594
utils/pub/io.dart:594: process.onError = completer.completeException;
On 2012/09/19 18:09:45, nweiz wrote:
> What happens if "tar" isn't found? Will onStart fire, then onError? If not,
the
> completer will never fire.

Good catch, thanks! If the executable is not found only 'onError' will fire.
I'll move the onError and onExit handler registration out of onStart and commit
separately.