Check that duplicate resources at different scale levels aren't in the same pak file

[GoogleCodeExporter]

(As talked about on IM with thakis@.)

Chrome has multiple resource paks for different purposes. There is a set of 
{default,touch}_{100,200,300,...}.pak files which contain data which is 
supposed to be keyed to certain properties of the display, and a normal 
resource.pak which is a supposed to be used for items which aren't display 
dependent.

It is entirely possible to enter a world of pain by unintentionally mixing 
these two concepts. Given that the definitions for, ie, the chrome_html and 
chrome_scaled_image structures live in grit, maybe a warning or error could be 
emitted if there's mixing of a chrome_scaled_image structure and a normal, 
non-image include?

This may not be possible (or adding this here might be the wrong architectural 
layer).

Original issue reported on code.google.com by [email protected] on 13 Apr 2015 at 11:51