Add Sensor.hasReading attribute

ED: https://w3c.github.io/sensors/#dom-sensor-hasreading

Bug: 750018
Change-Id: If9ffbd23c3e1eea66fe815792dd5e3b2ff3214ca
Reviewed-on: https://chromium-review.googlesource.com/684437
Reviewed-by: Alexander Shalamov <alexander.shalamov@intel.com>
Commit-Queue: Mikhail Pozdnyakov <mikhail.pozdnyakov@intel.com>
Cr-Commit-Position: refs/heads/master@{#504620}
6 files changed