Ensure original parser context is used when parsing resolved var() references

third_party/WebKit/LayoutTests/fast/css/resources/image-url-var.css

+.background.image-set.var {
+  --test: url('test.png');
+  background: -webkit-image-set(var(--test) 1x);
+}
+.background.image-set.inline {
+  background: -webkit-image-set(url('test.png') 1x);
+}
+
+.background.url.var {
+  --test: url('test.png');
+  background: var(--test);
+}
+.background.url.inline {
+  background: url('test.png');
+}
+
+.background-image.image-set.var {
+  --test: url('test.png');
+  background-image: -webkit-image-set(var(--test) 1x);
+}
+.background-image.image-set.inline {
+  background-image: -webkit-image-set(url('test.png') 1x);
+}
+
+.background-image.url.var {
+  --test: url('test.png');
+  background-image: var(--test);
+}
+.background-image.url.inline {
+  background-image: url('test.png');
+}