Fixes styling tests related to using HTML Imports

* [styling-scoped.html] remove test for <link rel="import" type="css"> as this is no longer supported
* [custom-style-async.html] convert test that used importHref to use dynamic import

test/unit/custom-style-async-import.js

@@ -0,0 +1,31 @@
+import { Polymer } from '../../lib/legacy/polymer-fn.js';
+
+const $_documentContainer = document.createElement('div');
+
+$_documentContainer.innerHTML = `<custom-style>
+<style is="custom-style">
+  html {
+    --cs-blue: {
+      border : 8px solid blue;
+    };
+  }
+</style>
+</custom-style>
+<dom-module id="x-client">
+<template>
+  <style>
+    :host {
+      display: inline-block;
+      border : 4px solid red;
+      @apply (--cs-blue);
+    }
+  </style>
+  x-client
+</template>
+</dom-module>`;
+
+document.body.appendChild($_documentContainer);
+
+Polymer({
+  is: 'x-client'
+});

test/unit/custom-style-async.html

@@ -48,7 +48,7 @@
 suite('async global custom-style', function() {
 
   test('async loaded custom-style applies', function(done) {
-    host.importHref('custom-style-async-import.html', function() {
+    import('custom-style-async-import.js').then(() => {
       afterNextRender(null, function() {
         assertComputed(host.$.client, '8px');
         done();

test/unit/styling-scoped.html

@@ -687,19 +687,6 @@
 </script>
   </dom-module>
 
-  <dom-module id="x-only-link-style">
-    <link rel="import" type="css" href="styling-import-host.css">
-    <link rel="import" type="css" href="styling-import-host2.css">
-    <template></template>
-    <script type="module">
-import { PolymerElement } from '../../polymer-element.js';
-class XOnlyLink extends PolymerElement {
-  static get is() { return 'x-only-link-style'; }
-}
-customElements.define(XOnlyLink.is, XOnlyLink);
-</script>
-  </dom-module>
-
   <dom-module id="double-shared-style">
     <template>
       <style>
@@ -1006,12 +993,6 @@
     assertComputed(e, '5px', 'padding-top');
   });
 
-  test('elements without styles work', function() {
-    var e = document.createElement('x-only-link-style');
-    document.body.appendChild(e);
-    assertComputed(e, '2px');
-  });
-
 });
 
 suite('double including style sheets', function() {