Add UTF-8 DCHECK()s in values.cc (since keys/paths are expected to be UTF-8).
Add UTF-8 DCHECK()s in values.cc (since keys/paths are expected to be UTF-8).

BUG=23581
TEST=unit tests pass

Review URL: http://codereview.chromium.org/3081018

git-svn-id: http://src.chromium.org/svn/trunk/src@55190 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 3f1032dd703c944a5050a782e877ef568a749e2a
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