Teach mojo_shell how to load data URLs

Teach mojo_shell how to load data URLs

This CL contains enough integration with net to load data URLs. A future CL
will add the ability to load http and https URLs. Data URLs are easier because
they're entirely in-memory.

R=aa@chromium.org

[abarth-chromium, 2013-10-17 23:34:35]

Let me know where you'd like this code to go.  I put it in a new directory
because experience tells me that the loader machinery will grow a bit.  :)

[abarth-chromium, 2013-10-17 23:55:22]

+darin in case he has opinions on where this code should live.

[abarth-chromium, 2013-10-18 06:50:52]

Closing this issue.  I'm going to roll this all into
https://codereview.chromium.org/27943002/.