Failing gracefully

added a catch error to avoid printing a stack trace when it fails to create a mirror system.

R=amouravski@google.com

Committed: https://code.google.com/p/dart/source/detail?r=24650

[Andrei Mouravski, 2013-06-28 22:57:34]

https://codereview.chromium.org/18237002/diff/2001/pkg/docgen/lib/docgen.dart
File pkg/docgen/lib/docgen.dart (right):

https://codereview.chromium.org/18237002/diff/2001/pkg/docgen/lib/docgen.dart...
pkg/docgen/lib/docgen.dart:189: exit(1);
I think you can actually extract the stack trace in the new system, though I'm
not sure... Ask Nathan or Bob.

[janicejl, 2013-06-28 23:47:12]

https://codereview.chromium.org/18237002/diff/2001/pkg/docgen/lib/docgen.dart
File pkg/docgen/lib/docgen.dart (right):

https://codereview.chromium.org/18237002/diff/2001/pkg/docgen/lib/docgen.dart...
pkg/docgen/lib/docgen.dart:189: exit(1);
On 2013/06/28 22:57:34, Andrei Mouravski wrote:
> I think you can actually extract the stack trace in the new system, though I'm
> not sure... Ask Nathan or Bob.

Have talked to Nathan. 

Dart2js analyze throws a string when it fails to create a mirror system, and
hence it is not possible to use the stack trace package to extract fine details
about the error.

[Andrei Mouravski, 2013-06-29 06:46:07]

lgtm

[janicejl, 2013-07-01 19:58:42]

Committed patchset #4 manually as r24650 (presubmit successful).