Function scopes only must have a context if they call sloppy eval

Function scopes only must have a context if they call sloppy eval

A strict arrow function with no parameters and no variable bindings
won't need a context object because it will never have any
locals.  (This is unlike strict normal functions, which do have
"arguments" and "this" locals.)

R=rossberg@chromium.org
BUG=v8:4056
LOG=N

Review URL: https://codereview.chromium.org/1093183003

Cr-Commit-Position: refs/heads/master@{#28031}