Add VC++ 2015 file to .gitignore

Add VC++ 2015 file to .gitignore

When using VC++ 2015 Update 1 RC the IDE drops *.VC.opendb files which
then clutter the git status update like this:

Untracked files:
  (use "git add <file>..." to include in what will be committed)

        chrome_dev.VC.opendb

This change tells git to ignore them.

BUG=440500
Committed: https://crrev.com/23e5ea254fea6ad3618588f177406640e7104d38
Cr-Commit-Position: refs/heads/master@{#358163}

[brucedawson, 2015-11-05 22:19:43]

brucedawson@chromium.org changed reviewers:
+ scottmg@chromium.org

[brucedawson, 2015-11-05 22:19:44]

Minor tweak for Update 1 RC

[scottmg, 2015-11-05 22:40:26]

lgtm

[brucedawson, 2015-11-05 22:48:39]

The CQ bit was checked by brucedawson@chromium.org

[commit-bot: I haz the power, 2015-11-05 22:49:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1413153015/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1413153015/20001

[commit-bot: I haz the power, 2015-11-05 23:04:44]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-05 23:05:51]

Patchset 2 (id:??) landed as
https://crrev.com/23e5ea254fea6ad3618588f177406640e7104d38
Cr-Commit-Position: refs/heads/master@{#358163}