Port 2b4cb2a1

Original commit message:
    The %StringCharFromCode and %CharFromCode runtime function perform
    exactly the same task, so we need only one of them.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1429953005

Cr-Commit-Position: refs/heads/master@{#31904}