[Sensors] Read-only access to the sensors shared buffer from Blink

Provide read-only access to the sensors shared buffer for the Blink-side clients (i.e. JS sensor instances).

BUG=606766

Review-Url: https://codereview.chromium.org/2417533002
Cr-Commit-Position: refs/heads/master@{#424741}
1 file changed