Bug 1363998 - Skip the reftests for advanced background-color layers if WebRender is not enabled. r=bustage

On Windows with webrender disabled and advanced background-color layers enabled,
these tests fail because they have a higer fuzz than allowed. Specifically:

1316719-1a.html -> max difference: 53, number of differing pixels: 785
1316719-1b.html -> max difference: 53, number of differing pixels: 785
1316719-1c.html -> max difference: 53, number of differing pixels: 787

I'm assuming that for now we only care about the advanced background-color layers
when WebRender is enabled, so we can just skip the tests otherwise.

MozReview-Commit-ID: 3HI828mcBdH

layout/reftests/bugs/reftest.list

@@ -1987,9 +1987,9 @@ fuzzy(2,20000) == 1315113-2.html 1315113-2-ref.html
 fuzzy(2,40000) == 1316719-1a.html 1316719-1-ref.html
 fuzzy(2,40000) == 1316719-1b.html 1316719-1-ref.html
 fuzzy(2,40000) == 1316719-1c.html 1316719-1-ref.html
-pref(layers.advanced.background-color,1) fuzzy-if(!webrender,2,40000) fuzzy-if(webrender,27,700) == 1316719-1a.html 1316719-1-ref.html
-pref(layers.advanced.background-color,1) fuzzy-if(!webrender,2,40000) fuzzy-if(webrender,27,700) == 1316719-1b.html 1316719-1-ref.html
-pref(layers.advanced.background-color,1) fuzzy-if(!webrender,2,40000) fuzzy-if(webrender,27,700) == 1316719-1c.html 1316719-1-ref.html
+pref(layers.advanced.background-color,1) skip-if(!webrender) fuzzy-if(webrender,27,700) == 1316719-1a.html 1316719-1-ref.html
+pref(layers.advanced.background-color,1) skip-if(!webrender) fuzzy-if(webrender,27,700) == 1316719-1b.html 1316719-1-ref.html
+pref(layers.advanced.background-color,1) skip-if(!webrender) fuzzy-if(webrender,27,700) == 1316719-1c.html 1316719-1-ref.html
 skip-if(Android) != 1318769-1.html 1318769-1-ref.html
 fails-if(stylo) == 1322512-1.html 1322512-1-ref.html
 == 1330051.svg 1330051-ref.svg