Redirect chrome://welcome to the new tab page.

Redirect chrome://welcome to the new tab page.

The welcome page was removed in M40. Users who had the welcome page open
when upgrading from pre-M40 to post-M40 will see a "webpage not
available" error after the upgrade. This fixes that behavior by
replacing the welcome page with an NTP.

BUG=455427
Committed: https://crrev.com/4bdfb4b68b800911adb3d36d64e841fa6ec5757a
Cr-Commit-Position: refs/heads/master@{#322049}

[newt (away), 2015-03-24 18:28:17]

newt@chromium.org changed reviewers:
+ dtrainor@chromium.org

[newt (away), 2015-03-24 18:28:17]

PTAL

[Ted C, 2015-03-24 18:38:04]

tedchoc@chromium.org changed reviewers:
+ tedchoc@chromium.org

[Ted C, 2015-03-24 18:38:04]

lgtm

[newt (away), 2015-03-24 18:38:39]

The CQ bit was checked by newt@chromium.org

[commit-bot: I haz the power, 2015-03-24 18:39:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1036533002/1

[commit-bot: I haz the power, 2015-03-24 19:40:08]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-24 19:40:40]

Patchset 1 (id:??) landed as
https://crrev.com/4bdfb4b68b800911adb3d36d64e841fa6ec5757a
Cr-Commit-Position: refs/heads/master@{#322049}