Fix "inherited from" comments for Interceptor

Add a snapshot for docgen and use it in the build (https://codereview.chromium.org/116043013/)

Also fixed up comments for some inherited object methods.


BUG=
R=alanknight@google.com

Committed: https://code.google.com/p/dart/source/detail?r=31850

[Emily Fortuna, 2014-01-15 07:21:00]

Hey Denmark folk, 
This is a reincarnation of Alan's CL from here:
https://codereview.chromium.org/116043013/ The changes *should be* identical to
what's in that CL if you do a delta-from-patchset-2-to-1. Please look over all
the files except don't worry about pkg/docgen/bin/docgen.dart, as Alan will
review that one. (small disclaimer that part of the CL -- I pretty much applied
Alan's patch wholesale, so Alan may be better suited to answer questions about
the functions)

Alan,
The changes that are NOT from your original CL are in Patch Set 1. So you only
need to review that file pkg/docgen/bin/docgen.dart

Thanks for taking a look-over, everyone!

[Emily Fortuna, 2014-01-15 18:26:11]

(removed the snapshotting change in the interest of getting this change in)

[Alan Knight, 2014-01-15 19:13:24]

lgtm

[Emily Fortuna, 2014-01-15 21:13:01]

Committed patchset #3 manually as r31850 (presubmit successful).