Made Question Mark in browser settings overlay 2x friendly

Before: http://i.imgur.com/stKv9fc.png
After:  http://i.imgur.com/LPZ5fSf.png

BUG=310610

Review URL: https://codereview.chromium.org/39973002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230724 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230724