Correct bug in InitDeviceScaleFactor - hidden variable.

Bug was introduced during refactor in r225722

BUG=306268

Review URL: https://codereview.chromium.org/26444010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228107 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228107