Get rid of PrefService::GetMutableDictionary/GetMutableList
Get rid of PrefService::GetMutableDictionary/GetMutableList

BUG=77914
TEST=none, trybots remain green

Review URL: http://codereview.chromium.org/6691032

git-svn-id: http://src.chromium.org/svn/trunk/src@80442 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 44868376447b0b898d3ff35821aa82ad37faa12d
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser