Disable browser key reservation in fullscreen mode

In intent to implement https://goo.gl/4tJ32G, we decided to deliver browser
shortcuts to the websites, so a web page can provide almost consistent user
experience as a native application. To ensure there is no security risk, a
simple and safe approach is to allow websites to capture browser reserved
keyboard combinations in full screen mode only.
This does not apply to the keys to exit fullscreen (F11) or exit the
application (ESC).

BUG=680809

Review-Url: https://codereview.chromium.org/2636013002
Cr-Commit-Position: refs/heads/master@{#449896}
2 files changed