[sensors] Add layout test for sensor construction within iframe

According to the specificatoin [1], sensor objects must be exposed
only to the top level browsing context, this CL adds layout test
that verifies such constraint.

[1] https://w3c.github.io/sensors/#top-level-browsing-context

Bug: 606766
Change-Id: Ibd2ef5e92a062198793ce57a9e533e00745c5567
Reviewed-on: https://chromium-review.googlesource.com/559044
Commit-Queue: Alexander Shalamov <alexander.shalamov@intel.com>
Reviewed-by: Mikhail Pozdnyakov <mikhail.pozdnyakov@intel.com>
Cr-Commit-Position: refs/heads/master@{#484216}
1 file changed