[cssom-view] Window#outerWidth and Window#outerHeight don't have units specified

[gsnedders]

The current definition is:

The outerWidth attribute must return the width of the client window. If there is no client window this attribute must return zero.

This doesn't state what units the width of the client window is measured using.

We probably want:

The outerWidth attribute must return the width of the client window as a number of 'CSS pixels'. If there is no client window this attribute must return zero.

[Nadya678]

Like getComputedStyles, it works with CSS pixels. Is there any problem? Many CSSOM functions (inherited from old DHTML) has "no unit" (the unit is px). There is needed clarification and please add that the unit is CSS pixel.