Fix docgen Uri handling so it works on Windows.

Fix docgen Uri handling so it works on Windows.

BUG=dartbug.com/15287
R=alanknight@google.com, efortuna@google.com

Committed: https://code.google.com/p/dart/source/detail?r=30634

Committed: https://code.google.com/p/dart/source/detail?r=30644

[aam-me, 2013-11-24 04:31:44]

Hi,

  I bumped into docgen build problem on my Windows box.
  Have a fix here.

  Please take a look if you have a chance!

Thanks.

[Emily Fortuna, 2013-11-25 16:39:57]

lgtm, thanks! I had noticed a number of Windows issues with that code -- thanks
for the fixes!

[Alan Knight, 2013-11-25 17:32:37]

lgtm

I don't completely love the mixing and matching path and URI operations but we
were doing that anyway, this just changes the ratio slightly.

[aam-me, 2013-11-25 17:33:43]

Committed patchset #1 manually as r30634 (presubmit successful).

[aam-me, 2013-11-25 18:39:30]

Thank you for the review, Alan, Emily.
I had to revert patchset #1 because of test failure.

I fixed it patchset #2 and have ran tests(tools/test.py -mrelease) in mac, win
and linux environments.

PTAL

[Alan Knight, 2013-11-25 18:41:44]

lgtm

[Emily Fortuna, 2013-11-25 20:07:50]

lgtm

[aam-me, 2013-11-25 21:00:00]

Committed patchset #2 manually as r30644 (presubmit successful).