Need an API to pause media playback for a webview

[Olivier Tilloy]

For applications running on handheld devices in staged mode, it is not uncommon to expect that a webview that has been backgrounded will pause its media playback, at least video. This is the case in webbrowser-app when switching between open tabs, and we are now working on adding multiple window support to the app, so we’ll want to pause all media playback for everything but the foreground window.

Not sure whether we want oxide to decide itself what to pause and when, or whether a public API to allow embedders to request pausing/resuming the playback at will is better.