Add var css function name to safestyle allowlist.

https://developer.mozilla.org/en-US/docs/Web/CSS/var()

Note that safestyle doesn't currently allow nested function calls in the args list.
RELNOTES: Add `var` css function name to safestyle allowlist.
PiperOrigin-RevId: 385539515
Change-Id: If05e81d6bc6bff516960a41b1530869ae75913ae

closure/goog/html/safestyle.js

@@ -534,6 +534,7 @@ const ALLOWED_FUNCTIONS = [
   'rgb',
   'rgba',
   '(rotate|scale|translate)(X|Y|Z|3d)?',
+  'var',
 ];
 
 

closure/goog/html/safestyle_test.js

@@ -176,6 +176,15 @@ testSuite({
         {'transform': 'translateX(5px)'});
   },
 
+  testCreate_allowsVar() {
+    assertCreateEquals(
+        'color:var(--xyz);',  // expected
+        {'color': 'var(--xyz)'});
+    assertCreateEquals(
+        'color:var(--xyz, black);',  // expected
+        {'color': 'var(--xyz, black)'});
+  },
+
   testCreate_allowsSafeUrl() {
     assertCreateEquals('background:url("http://example.com");', {
       'background': SafeUrl.fromConstant(Const.from('http://example.com')),