chrome: Simplify CPP files regex.

chrome: Simplify CPP files regex.

This regex can be simplified down to a single-one.

Similar to the way we already do elsewhere, like in //cc
(https://chromium.googlesource.com/chromium/src/+/master/cc/PRESUBMIT.py) and
ui/app_list
(https://chromium.googlesource.com/chromium/src/+/master/ui/app_list/PRESUBMIT.py)

BUG=None
TEST=git cl presubmit -uv
R=thestig@chromium.org

Committed: https://crrev.com/6aed9aec2e85c226de6b024bd4d253dea7d95e86
Cr-Commit-Position: refs/heads/master@{#319573}

[Lei Zhang, 2015-03-07 00:37:30]

lgtm

[tfarina, 2015-03-07 21:13:05]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-03-07 21:13:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/984073005/1

[commit-bot: I haz the power, 2015-03-07 23:14:30]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-03-07 23:14:31]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_TIMED_OUT, no build URL)
Timed out jobs are not retried to avoid causing additional load on the builders
with large pending queues.

[tfarina, 2015-03-07 23:50:19]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-03-07 23:50:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/984073005/1

[commit-bot: I haz the power, 2015-03-08 03:54:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-08 03:55:09]

Patchset 1 (id:??) landed as
https://crrev.com/6aed9aec2e85c226de6b024bd4d253dea7d95e86
Cr-Commit-Position: refs/heads/master@{#319573}