Reapply "Stop suppressing generation of bindings with Promise. Add some tests for DOM APIs that ans…

tests/html/fontface_loaded_test.dart

+library fontface_loaded_test;
+
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+
+import 'dart:async';
+import 'dart:isolate';
+import 'dart:html';
+
+class NullTreeSanitizer implements NodeTreeSanitizer {
+    void sanitizeTree(Node node) {}
+}
+
+main() {
+  useHtmlConfiguration();
+
+  var style = new Element.html('''
+      <style>
+      @font-face {
+        font-family: 'Ahem';
+        src: url(../../resources/Ahem.ttf);
+        font-style: italic;
+        font-weight: 300;
+        unicode-range: U+0-3FF;
+        font-variant: small-caps;
+        -webkit-font-feature-settings: "dlig" 1;
+        /* font-stretch property is not supported */
+      }
+      </style>
+      ''', treeSanitizer: new NullTreeSanitizer());
+  document.head.append(style);
+
+
+  test('document fonts - temporary', () {
+    var atLeastOneFont = false;
+    document.fonts.forEach((FontFace fontFace, _, __) {
+      atLeastOneFont = true;
+      Future f1 = fontFace.loaded;
+      Future f2 = fontFace.loaded;
+      expect(f1, equals(f2)); // Repeated calls should answer the same Future.
+
+      expect(fontFace.load(), throws);
+    });
+    expect(atLeastOneFont, isTrue);
+  });
+}