Make cross origin property conform to the Web IDL for same origin

Currently cross origin property returns the function of access source,
but according to the HTML standard it should return the function of access destination when the origins are the same origin.
This CL fixed the gap.

Bug: 809011
Change-Id: I474083b22cc11c162dab1c14e41bc328c9cadcad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1732751
Commit-Queue: Marina Sakai <marinasakai@google.com>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683910}