Bug 1503171 [wpt PR 13772] - Sync Mozilla CSS tests as of 2018-10-30, a=testonly

Automatic update from web-platform-testsSync Mozilla CSS tests as of https://hg.mozilla.org/mozilla-central/rev/6e4537056d5363fc118fa946615955798892314b . (#13772)

This contains changes from [bug 1502510](https://bugzilla.mozilla.org/show_bug.cgi?id=1502510) by @dholbert, reviewed by @heycam.
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wpt-commits: 1f06d26817ca7f03f3d42246fa1e14285e3aaecc
wpt-pr: 13772

testing/web-platform/tests/css/vendor-imports/mozilla/mozilla-central-reftests/values3/calc-background-position-1-ref.html

@@ -9,7 +9,7 @@
 p {
     height: 50px; width: 200px;
     border: thin solid;
-    background-image: url(../backgrounds/blue-32x32.png);
+    background-image: url(support/blue-32x32.png);
     background-repeat: no-repeat;
 }
 

testing/web-platform/tests/css/vendor-imports/mozilla/mozilla-central-reftests/values3/calc-background-position-1.html

@@ -11,7 +11,7 @@
 p {
     height: 50px; width: 200px;
     border: thin solid;
-    background-image: url(../backgrounds/blue-32x32.png);
+    background-image: url(support/blue-32x32.png);
     background-repeat: no-repeat;
 }
 

testing/web-platform/tests/css/vendor-imports/mozilla/mozilla-central-reftests/values3/calc-background-size-1-ref.html

@@ -9,7 +9,7 @@
 p {
     height: 50px; width: 200px;
     border: thin solid;
-    background-image: url(../backgrounds/blue-32x32.png);
+    background-image: url(support/blue-32x32.png);
     background-repeat: no-repeat;
 }
 

testing/web-platform/tests/css/vendor-imports/mozilla/mozilla-central-reftests/values3/calc-background-size-1.html

@@ -11,7 +11,7 @@
 p {
     height: 50px; width: 200px;
     border: thin solid;
-    background-image: url(../backgrounds/blue-32x32.png);
+    background-image: url(support/blue-32x32.png);
     background-repeat: no-repeat;
 }