grit: Use new --write-only-new flag.

grit: Use new --write-only-new flag.

For the file I'm testing with (c/b/resources/about_stats.html),
a rebuild runs 101 edges and compiles a bunch of cc files and takes 40s.
This reduces build times from 40s to 9.6s and reduces the number
of edges to 37.

BUG=439182
R=brettw@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/9261dde33f1939f432cafe6f9654efedba4dc252

[Nico, 2014-12-04 23:47:29]

thakis@chromium.org changed reviewers:
+ brettw@chromium.org, newt@chromium.org

[brettw, 2014-12-04 23:50:00]

lgtm

[Nico, 2014-12-05 00:04:15]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2014-12-05 00:04:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/740463005/20001

[commit-bot: I haz the power, 2014-12-05 00:50:42]

Patchset 2 (id:??) landed as
https://crrev.com/9261dde33f1939f432cafe6f9654efedba4dc252
Cr-Commit-Position: refs/heads/master@{#306945}

[Nico, 2014-12-05 00:50:53]

Committed patchset #2 (id:20001) manually as
9261dde33f1939f432cafe6f9654efedba4dc252 (presubmit successful).