Rendering notifications with different pixel densities

Hi,

While developing the notifications API for Chrome extensions, I've come
across a need to specify images with multiple representations for devices
that support high DPI displays.  A good example for this is a Chromebook
Pixel, which supports changing the device's effective pixel density on the
fly using a keyboard shortcut.

In order to support changing the scale factor dynamically, an extension
must have a way to specify (for example) a 1x and a 2x version of each
image in the notification ahead of time.  You could imagine other devices
supporting even more scale factors.

Even if you consider a static display configuration, there could be bugs in
the current spec for web notifications.  An example of this is a setup
where a 2x laptop (like a Retina MacBook) is connected to a 1x external
display.  In this case, a webpage may be displayed on the 1x display,
causing the user agent to report a devicePixelRatio of 1.  Then a created
notification may be displayed on the primary laptop (2x) display with the
wrong image.

Are there any plans to support multiple scale factors for image resources
in the web notifications API?  I'd like to conform as much as possible for
Chrome's extension API.

Thanks,
Justin