Add support for attaching observatory to the server

Add support for attaching observatory to the server.

R=paulberry@google.com, scheglov@google.com

Committed: https://code.google.com/p/dart/source/detail?r=41267

[Brian Wilkerson, 2014-10-23 16:41:20]

brianwilkerson@google.com changed reviewers:
+ paulberry@google.com, scheglov@google.com

[scheglov, 2014-10-23 17:56:30]

LGTM

[Paul Berry, 2014-10-23 18:02:11]

lgtm

https://codereview.chromium.org/651243005/diff/1/pkg/analysis_server/test/int...
File pkg/analysis_server/test/integration/integration_tests.dart (right):

https://codereview.chromium.org/651243005/diff/1/pkg/analysis_server/test/int...
pkg/analysis_server/test/integration/integration_tests.dart:702: //     
arguments.add('--enable-vm-service');
Were these commented-out lines left in on purpose or by accident?  If they're
left in on purpose, it would be nice to have a comment explaining what they are
there for.

[Brian Wilkerson, 2014-10-23 18:56:19]

https://codereview.chromium.org/651243005/diff/1/pkg/analysis_server/test/int...
File pkg/analysis_server/test/integration/integration_tests.dart (right):

https://codereview.chromium.org/651243005/diff/1/pkg/analysis_server/test/int...
pkg/analysis_server/test/integration/integration_tests.dart:702: //     
arguments.add('--enable-vm-service');
> Were these commented-out lines left in on purpose or by accident?

Sort of on purpose in that when I first uploaded I wasn't intending to commit
as-is so I didn't bother cleaning them up. But I'll remove them before
committing.

[Brian Wilkerson, 2014-10-23 19:18:17]

Committed patchset #1 (id:1) manually as 41267 (presubmit successful).