Fix left trimming check for large objects

BUG=358090
TEST=test/mjsunit/regress/regress-358090.js
LOG=N
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/213833008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20362 ce2b1a6d-e550-0410-aec6-3dcde31c8c00