IndexedDB: Rethrow exceptions thrown by getters during keypath eval

      BUG=493860
R=cmumford@chromium.org,haraken@chromium.org

Review URL: https://codereview.chromium.org/1154873007

git-svn-id: svn://svn.chromium.org/blink/trunk@196355 bbb929c8-8fbe-4397-9dbb-9b2b20218538