Introduce a new, cross-browser HiDPI CSS @media rule to be used everywhere.

{{{
@media print,
  (-o-min-device-pixel-ratio: 5/4),
  (-webkit-min-device-pixel-ratio: 1.25),
  (min-resolution: 120dpi) {
}}}

Serve HiDPI graphics for printing, regardless of screen resolution.

Specify Opera's vendor-prefixed device pixel ratio property, for Opera desktop.

Specify a minimum Webkit device pixel ratio of 1.25 instead of 1.5, to serve
2x images to Android devices that are between 1 and 1.5x (like the Nexus 7).
Firefox and Opera will respond to 1.5x on these devices, but Chrome will not.

Specify min-resolution, which covers Firefox 19. Opera on Android also supports
min-resolution, but Opera Mini does not support dppx, so the dpi unit is used.

props iammattthomas for the exhaustive research.
props lessbloat for patching.

fixes #22238.



git-svn-id: https://develop.svn.wordpress.org/trunk@22629 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/css/wp-pointer.css

@@ -189,7 +189,10 @@
 /**
  * HiDPI Displays
  */
-@media only screen and (-webkit-min-device-pixel-ratio: 1.5) {
+@media print,
+  (-o-min-device-pixel-ratio: 5/4),
+  (-webkit-min-device-pixel-ratio: 1.25),
+  (min-resolution: 120dpi) {
 
 	.wp-pointer-buttons a.close:before {
 		background-image: url('../images/xit-2x.gif');