[Sensors] start() and stop() methods do not throw

Instead, these methods should use "Handle Errors" operation (https://w3c.github.io/sensors/#handle-errors) for error handling consistency.

BUG=606766

Review-Url: https://codereview.chromium.org/2684743003
Cr-Commit-Position: refs/heads/master@{#449247}
3 files changed