[sensors] [win] Fix ambient light not working properly on Windows 10.

The event listener was never called despite SetEventSink returning
success. Debbuging further it turns out that the event listener was
created in the sensor thread, however the listener was not set in
the sensor thread (from StartSensor()), this seems to confuse COM.

BUG=606766

Review-Url: https://codereview.chromium.org/2495073002
Cr-Commit-Position: refs/heads/master@{#435513}
3 files changed