Use reasonable defaults for docgen if invoked on a single package

Use reasonable defaults for docgen if invoked on a single package

BUG=
R=efortuna@google.com

Committed: https://code.google.com/p/dart/source/detail?r=32583

[Emily Fortuna, 2014-02-11 22:35:32]

https://codereview.chromium.org/158833005/diff/10001/pkg/docgen/bin/docgen.dart
File pkg/docgen/bin/docgen.dart (right):

https://codereview.chromium.org/158833005/diff/10001/pkg/docgen/bin/docgen.da...
pkg/docgen/bin/docgen.dart:25: String get _defaultStartPage {
nit: I'd put this function down below the main, so that the main is at the top,
aside from the global variables.

https://codereview.chromium.org/158833005/diff/10001/pkg/docgen/bin/docgen.da...
pkg/docgen/bin/docgen.dart:52: options = _initArgParser().parse(arguments);
I think you're missing some logic here.  (or I'm misreading this) The only place
this result is used seems to be in _defaultStartPage. If you're re-parsing,
don't you want to use that result somewhere in your parse?  Also can't we always
do this by default?

[Alan Knight, 2014-02-11 23:01:55]

The logic was more complicated than it needed to be now that we're only really
setting the start-page option based on this. Simplified it.

[Emily Fortuna, 2014-02-11 23:44:06]

lgtm!

[Alan Knight, 2014-02-11 23:45:13]

Committed patchset #3 manually as r32583 (presubmit successful).