Port 12bcba15

Original commit message:
    The API functions are always in sloppy mode, so receiver is always a
    JSReceiver once the actual call trampoline runs, no need to check again
    in various places.

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

Review URL: https://codereview.chromium.org/1583893002

Cr-Commit-Position: refs/heads/master@{#33273}