This fixes data-flow tracking of sub-word (i.e. int8 or int16) element
accesses withing the escape analysis. In essense this makes sure that
we only ever consider the offset for loads and stores on tracked objects
and avoid mangling the offset on untracked ones.

R=jarin@chromium.org
TEST=cctest/test-api/Fixed[U]Int[8,16]Array

Review-Url: https://codereview.chromium.org/2008883002
Cr-Commit-Position: refs/heads/master@{#36573}