Ensure initial static classes are preserved when a class$ binding is …

…present

This ensures ShadyCSS scoping classes are not removed when a class binding's initial literal value is set.

lib/mixins/property-effects.js

@@ -2543,6 +2543,11 @@ export const PropertyEffects = dedupingMixin(superClass => {
         // Initialize attribute bindings with any literal parts
         let literal = literalFromParts(parts);
         if (literal && kind == 'attribute') {
+          // Ensure a ShadyCSS template scoped style is not removed
+          // when a class$ binding's initial literal value is set.
+          if (name == 'class' && node.hasAttribute('class')) {
+            literal += ' ' + node.getAttribute(name);
+          }
           node.setAttribute(name, literal);
         }
         // Clear attribute before removing, since IE won't allow removing

test/unit/styling-scoped.html

@@ -153,6 +153,18 @@
 </script>
 </dom-module>
 
+<dom-module id="x-class-literal">
+  <template>
+    <div id="scope" class$="a [[b]] c" class="d e">Trivial</div>
+  </template>
+  <script type="module">
+import { Polymer } from '../../polymer-legacy.js';
+Polymer({
+  is: 'x-class-literal'
+});
+</script>
+</dom-module>
+
 
 
 <dom-module id="x-styled">
@@ -993,6 +1005,17 @@
     assertComputed(e, '5px', 'padding-top');
   });
 
+  test('initial literal values in class are preserved when a class$ binding is present', function() {
+    var e = document.createElement('x-class-literal');
+    document.body.appendChild(e);
+    var el = e.$.scope;
+    assert.equal(el.classList.length, 4);
+    assert.isTrue(el.classList.contains('a'));
+    assert.isTrue(el.classList.contains('c'));
+    assert.isTrue(el.classList.contains('d'));
+    assert.isTrue(el.classList.contains('e'));
+  });
+
 });
 
 suite('double including style sheets', function() {