We block constant pool up to the call stub instruction, but the check for code size
includes the next instruction after the call instruction. That instruction can
emit constant pool.

BUG=chromium:500831
LOG=NO
TEST=mjsunit/regress/regress-500831

Review URL: https://codereview.chromium.org/1189123003

Cr-Commit-Position: refs/heads/master@{#29132}