Removed isEmpty function.
Removed isEmpty function.

As it is not clear what 'isEmpty' refers to with this type of stack implementation, it is better to be explicit with the
conditions.

R=mgiuca@chromium.org

Review URL: https://codereview.appspot.com/200780043

jackhou-chromium/bitmapper,jackhou-chromium/bitmapper,jackhou-chromium/bitmapper