Fix long-skipped test

Author: kevmoo

test/model_test.dart

@@ -461,11 +461,11 @@ void main() {
 
       test('links to a top-level variable with a prefix from an imported lib',
           () {
-        expect(docsAsHtml,
-            contains('<a href="">css.theOnlyThingInTheLibrary</a>'));
-      },
-          skip:
-              'Wait for https://github.com/dart-lang/dartdoc/issues/767 to be fixed');
+        expect(
+            docsAsHtml,
+            contains(
+                '<a href="ex/incorrectDocReferenceFromEx-constant.html">example_prefixed.incorrectDocReferenceFromEx</a>'));
+      });
 
       // remove this test when the above test is fixed. just here to
       // track when the behavior changes

testing/test_package/lib/fake.dart

@@ -52,7 +52,7 @@ import 'dart:collection';
 
 import 'example.dart';
 
-import 'css.dart' as css;
+import 'example.dart' as example_prefixed;
 
 import 'two_exports.dart' show BaseClass;
 
@@ -496,7 +496,7 @@ class BaseForDocComments {
   ///
   /// Reference to a top-level const in another library [incorrectDocReferenceFromEx]
   ///
-  /// Reference to prefixed-name from another lib [css.theOnlyThingInTheLibrary] xx
+  /// Reference to prefixed-name from another lib [example_prefixed.incorrectDocReferenceFromEx]
   ///
   /// Reference to a name that exists in this package, but is not imported
   /// in this library [doesStuff] xx

testing/test_package_docs/fake/BaseForDocComments/doAwesomeStuff.html

@@ -80,7 +80,7 @@ <h5>class BaseForDocComments</h5>
 <p>Reference to a top-level const in this library that shares the same
 name as a top-level name in another library <a href="fake/incorrectDocReference-constant.html">incorrectDocReference</a> xx</p>
 <p>Reference to a top-level const in another library <a href="ex/incorrectDocReferenceFromEx-constant.html">incorrectDocReferenceFromEx</a></p>
-<p>Reference to prefixed-name from another lib <a href="css/theOnlyThingInTheLibrary.html">css.theOnlyThingInTheLibrary</a> xx</p>
+<p>Reference to prefixed-name from another lib <a href="ex/incorrectDocReferenceFromEx-constant.html">example_prefixed.incorrectDocReferenceFromEx</a></p>
 <p>Reference to a name that exists in this package, but is not imported
 in this library <a href="anonymous_library/doesStuff.html">doesStuff</a> xx</p>
 <p>Reference to a name of a class from an import of a library that exported