[sensors] Blink-side implementation of mojo interfaces

This patch introduces blink-side implementation of generic
sensor mojo interfaces.

Specification: https://w3c.github.io/sensors
Browser side CL: https://crrev.com/2144623003/

BUG=606766

Review-Url: https://codereview.chromium.org/2121313002
Cr-Commit-Position: refs/heads/master@{#416920}
7 files changed