Reintroduce plumbing for user gesture into permission system.

This will allow metrics to be gathered about the acceptance / denial
rates of permission prompts with gestures and without.

This effectively reverts:
1. https://crrev.com/acea72be67d92e56665f5357f4441f65c8073c15 and
2. https://crrev.com/a8e32b6fc3a4696ba24c8d6f257ec3fe848cf940

Those patches could not be reverted individually due to refactorings in
the permissions sytem.

TBR=torne@chromium.org
BUG=614599

Review-Url: https://codereview.chromium.org/2110343002
Cr-Commit-Position: refs/heads/master@{#403738}
49 files changed