[cssom-view-1] Name the algorithm for determining devicePixelRatio

...so that it can be called in non-Window contexts, by other specs

Author: eeeps

cssom-view-1/Overview.bs

@@ -629,7 +629,7 @@ The <dfn attribute for=Window>outerHeight</dfn> attribute must return the height
 client window. If there is no client window this
 attribute must return zero. <!--fingerprint-->
 
-The <dfn attribute for=Window caniuse=devicepixelratio>devicePixelRatio</dfn> attribute must return the result of the following algorithm:
+The <dfn attribute for=Window caniuse=devicepixelratio>devicePixelRatio</dfn> attribute must return the result of the following <dfn export>determine the device pixel ratio</dfn> algorithm:
 
 1. If there is no output device, return 1 and abort these steps.
 1. Let <var>CSS pixel size</var> be the size of a <a lt=px value>CSS pixel</a> at the current <a>page zoom</a> scale factor and at a <a>pinch zoom</a> scale factor of 1.0.