Port 306c412c

Original commit message:

    This is needed by Blink to implement the Custom Elements spec.

R=adamk@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=v8:4261
LOG=N

Review-Url: https://codereview.chromium.org/1929703002
Cr-Commit-Position: refs/heads/master@{#35838}