Add option to force document level passive event listeners as a runtime feature.

This approach removes the value from the override setting and allows it
to be set as a runtime feature.

Since field trial variations aren't supported in the renderer and only
the browser process adding an additional runtime enabled feature seems
the easiest approach forward.

BUG=625675

Review-Url: https://codereview.chromium.org/2125683002
Cr-Commit-Position: refs/heads/master@{#403972}
14 files changed