Refactoring: Move queryLocalizedString() to Locale class.

They always return strings for browser UI locale for now. We'd like to
update them so that they return locale-dependent strings in the future.

Also, remove unused functions of LocalizedStrings.

BUG=161733
TEST=none; no behavior changes.

Review URL: https://chromiumcodereview.appspot.com/24201005

git-svn-id: svn://svn.chromium.org/blink/trunk@158004 bbb929c8-8fbe-4397-9dbb-9b2b20218538