Bug 1858468 - Don't compute custom properties twice inside links. r=d…

…shin

This matches the behavior of other browsers (in fact, I filed [1] about
it long time ago).

This avoids a bunch of overhead in some speedometer subtests. Makes me a
bit sad because I still think our approach is slightly more correct per
spec, but not worth the performance cost.

[1]: w3c/csswg-drafts#2263

Differential Revision: https://phabricator.services.mozilla.com/D190705

UltraBlame original commit: e136cc9893278df1df3e3b997b9e6756122b9c44

layout/reftests/css-visited/variables-visited-ref.html

@@ -0,0 +1,33 @@
+<
+!
+doctype
+html
+>
+<
+style
+>
+a
+{
+color
+:
+green
+;
+}
+<
+/
+style
+>
+<
+a
+href
+=
+"
+"
+>
+Which
+color
+?
+<
+/
+a
+>

layout/reftests/css-visited/variables-visited.html

@@ -0,0 +1,59 @@
+<
+!
+doctype
+html
+>
+<
+style
+>
+a
+{
+-
+-
+foo
+:
+green
+;
+}
+:
+visited
+{
+-
+-
+foo
+:
+red
+;
+color
+:
+var
+(
+-
+-
+foo
+)
+;
+}
+<
+/
+style
+>
+<
+a
+href
+=
+"
+visited
+-
+page
+.
+html
+"
+>
+Which
+color
+?
+<
+/
+a
+>

layout/style/test/moz.build

@@ -1729,6 +1729,40 @@ css
 -
 visited
 /
+variables
+-
+visited
+-
+ref
+.
+html
+"
+"
+/
+layout
+/
+reftests
+/
+css
+-
+visited
+/
+variables
+-
+visited
+.
+html
+"
+"
+/
+layout
+/
+reftests
+/
+css
+-
+visited
+/
 visited
 -
 inherit

layout/style/test/test_visited_reftests.html

@@ -1765,6 +1765,22 @@
 .
 svg
 "
+"
+=
+=
+variables
+-
+visited
+.
+html
+variables
+-
+visited
+-
+ref
+.
+html
+"
 ]
 ;
 /