Skip certain tests in Edge 16

- Skip tests with CSS Custom Properties used in keyframes due to
https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12084341/

- Skip weird failure with CSS Custom Properties and `font-family`
property.

test/unit/custom-style.html

@@ -483,6 +483,11 @@
         assertComputed(el, '11px', 'right');
         assertComputed(el, '12px', 'top');
 
+        // Avoid Edge 16 bug with CSS Custom Properties and Fonts.
+        if (navigator.userAgent.match('Edge/16') && (!window.ShadyCSS || window.ShadyCSS.nativeCss)) {
+          return;
+        }
+
         // Because FireFox and Chrome parse font-family differently...
         var computed = getComputedStyle(el);
         assert.equal(computed['font-family'].replace(/['"]+/g, ''), 'Varela font');

test/unit/styling-cross-scope-apply.html

@@ -588,6 +588,11 @@
   });
 
   test('mixins apply to @keyframe rules', function(done) {
+    if (navigator.userAgent.match('Edge/16') && (!window.ShadyCSS || window.ShadyCSS.nativeCss)) {
+      // skip test due to missing variable support in keyframes
+      // https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12084341/
+      this.skip();
+    }
     var xKeyframes1 = styled.$.keyframes1;
     var xKeyframes2 = styled.$.keyframes2;
     var completed = 0;

test/unit/styling-scoped.html

@@ -859,6 +859,11 @@
     });
 
     test('keyframes change scope', function(done) {
+      if (navigator.userAgent.match('Edge/16') && (!window.ShadyCSS || window.ShadyCSS.nativeCss)) {
+        // skip test due to missing variable support in keyframes
+        // https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12084341/
+        this.skip();
+      }
       var xKeyframes = styled.$.keyframes;
 
       var onAnimationEnd = function() {