Fix Browser when running on a platform without webview

Fix Browser: can't access the WebIconDatabase. Added build version checks so
that the icon database isn't used on devices <= KITKAT: the entire class is
deprecated as of JB MR2 anyway, according to the comments.
Bug: 15088030

Change-Id: I4403b1a429c08abb288f5ee3bae7eb2e23303916