Improve quoting in pub reproduction command line in pub error message.

Improve quoting in pub reproduction command line in pub error message.

Windows users got an error because single quotes are not supported for
command line parameters.

BUG=dartbug.com/22992

Closed this CL and reopened as  https://codereview.chromium.org/1156663002/

[Bill Hesse, 2015-03-26 10:32:44]

whesse@google.com changed reviewers:
+ nweiz@google.com

[nweiz, 2015-03-26 21:46:21]

https://codereview.chromium.org/1035853003/diff/1/sdk/lib/_internal/pub/lib/s...
File sdk/lib/_internal/pub/lib/src/command_runner.dart (right):

https://codereview.chromium.org/1035853003/diff/1/sdk/lib/_internal/pub/lib/s...
sdk/lib/_internal/pub/lib/src/command_runner.dart:134: String
protectArgument(String x) => x.contains(' ') ? '"$x"' : x;
Can you add a TODO here to do proper shell escaping? Anything less than that is
still going to be a hack that fails sometimes.

Also, nit: we don't use type annotations in the bodies of method calls.

[Bill Hesse, 2015-05-22 08:00:06]

Comments addressed, and uploaded as new CL
https://codereview.chromium.org/1035853003/
rebased onto github repository.