Add markdown to third_party/pkg

third_party/pkg/markdown/test/markdown_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// Unit tests for markdown.
 library markdownTests;
 
 import 'package:unittest/unittest.dart';
 
 // TODO(rnystrom): Use "package:" URL (#4968).
@@ skipping 406 matching lines @@
         <pre><code>three</code></pre>
         ''');
 
     validate('escape HTML characters', '''
             <&>
         ''', '''
         <pre><code>&lt;&amp;&gt;</code></pre>
         ''');
   });
 
+  group('Fenced code blocks', () {
+    validate('without an optional language identifier', '''
+        ```
+        code
+        ```
+        ''', '''
+        <pre><code>code
+        </code></pre>
+        ''');
+
+    validate('with an optional language identifier', '''
+        ```dart
+        code
+        ```
+        ''', '''
+        <pre><code>code
+        </code></pre>
+        ''');
+
+    validate('escape HTML characters', '''
+        ```
+        <&>
+        ```
+        ''', '''
+        <pre><code>&lt;&amp;&gt;
+        </code></pre>
+        ''');
+  });
+
   group('Horizontal rules', () {
     validate('from dashes', '''
         ---
         ''', '''
         <hr />
         ''');
 
     validate('from asterisks', '''
         ***
         ''', '''
@@ skipping 466 matching lines @@
 
     // If one string runs out of non-ignored strings, the other must too.
     if (i == a.length) return j == b.length;
     if (j == b.length) return i == a.length;
 
     if (a[i] != b[j]) return false;
     i++;
     j++;
   }
 }