(branched from  issue 569981 )

If an app or extension uses chrome.power.requestKeepAwake to request that the system be kept awake or its screen stay on but fails to call releaseKeepAwake later, the request will stay active indefinitely.

This is probably reasonable in the case of a continuously-running extension, but it seems unexpected for an app that's attempting to tie its request to a window that can be closed. Specifically, we saw (and Lann fixed) an issue where Chrome OS's built-in video player didn't release its lock when its window was closed, resulting in the screen staying on.

In the implementation of the API, I tried to use OnExtensionUnloaded() to automatically release locks, but it turns out it's only called when the extension crashes or is disabled, uninstalled, or upgraded.

When I asked about this at https://groups.google.com/a/chromium.org/forum/#!topic/apps-dev/8Otp9etrT8I/discussion, Ken's recommendation was to make requestKeepAwake take an optional option tying the lifetime of the request to the caller's window.

I'm worried that this still requires callers to be aware of the issue and to do the right thing, and that if they're going to do that, they can just release the request when their window is closed instead.

So, I'd still like to find a way to handle window closure automatically if possible. Failing that, I ought to at least update the API docs to call out this subtlety.