v8binding: Use the incumbent realm instead of the current realm (Location)

Blink has been using the current realm as an approximation to
the incumbent realm.  Now the incumbent realm is almost ready
for real use, so this patch switches to use the incumbent realm.

This patch updates Location IDL interface.

Bug: 761755
Change-Id: I2070f46a3a86aa02950dd4ca45e6cb0b47f4326a
Reviewed-on: https://chromium-review.googlesource.com/c/1425854
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625541}
12 files changed