Duplicate parameters are banned both overall in strict mode and also
in arrow functions. Our error message for both cases blamed strict
mode, which is confusing. This patch fixes the message to point to
arrow functions as a possible source as well.
R=wingo, adamk
LOG=N
Review URL: https://codereview.chromium.org/1236863008
Cr-Commit-Position: refs/heads/master@{#29662}
This commit is a precursor to making lazy arrow function parsing use
similar logic to function(){} argument parsing.
R=arv@chromium.org
BUG=4020
LOG=N
Review URL: https://codereview.chromium.org/1078093002
Cr-Commit-Position: refs/heads/master@{#27773}