Add markdown to third_party/pkg

third_party/pkg/markdown/lib/src/markdown/block_parser.dart

Index: third_party/pkg/markdown/lib/src/markdown/block_parser.dart
diff --git a/sdk/lib/_internal/dartdoc/lib/src/markdown/block_parser.dart b/third_party/pkg/markdown/lib/src/markdown/block_parser.dart
similarity index 92%
copy from sdk/lib/_internal/dartdoc/lib/src/markdown/block_parser.dart
copy to third_party/pkg/markdown/lib/src/markdown/block_parser.dart
index bd14f36cad126cbd7255c06269bcc02bdd0a1578..42b93533345b9ab8ceae524a7a4c7c0f8ba47e16 100644
--- a/sdk/lib/_internal/dartdoc/lib/src/markdown/block_parser.dart
+++ b/third_party/pkg/markdown/lib/src/markdown/block_parser.dart
@@ -19,6 +19,9 @@ final _RE_BLOCKQUOTE = new RegExp(r'^[ ]{0,3}>[ ]?(.*)$');
 /// A line indented four spaces. Used for code blocks and lists.
 final _RE_INDENT = new RegExp(r'^(?:    |\t)(.*)$');
 
+/// GitHub style triple quoted code block.
+final _RE_CODE = new RegExp(r'^```(.*)$');
+
 /// Three or more hyphens, asterisks or underscores by themselves. Note that
 /// a line like `----` is valid as both HR and SETEXT. In case of a tie,
 /// SETEXT should win.
@@ -94,6 +97,7 @@ abstract class BlockSyntax {
           new SetextHeaderSyntax(),
           new HeaderSyntax(),
           new CodeBlockSyntax(),
+          new GitHubCodeBlockSyntax(),
           new BlockquoteSyntax(),
           new HorizontalRuleSyntax(),
           new UnorderedListSyntax(),
@@ -240,6 +244,42 @@ class CodeBlockSyntax extends BlockSyntax {
   }
 }
 
+/// Parses preformatted code blocks between two ``` sequences.
+class GitHubCodeBlockSyntax extends BlockSyntax {
+  RegExp get pattern => _RE_CODE;
+
+  List<String> parseChildLines(BlockParser parser) {
+    final childLines = <String>[];
+    parser.advance();
+    while (!parser.isDone) {
+      var match = pattern.firstMatch(parser.current);
+      if (match == null) {
+        childLines.add(parser.current);
+        parser.advance();
+      } else {
+        parser.advance();
+        break;
+      }
+    }
+    return childLines;
+  }
+
+  Node parse(BlockParser parser) {
+    // Get the syntax identifier, if there is one.
+    var syntax = pattern.firstMatch(parser.current).group(1);
+    
+    final childLines = parseChildLines(parser);
+
+    // The Markdown tests expect a trailing newline.
+    childLines.add('');
+
+    // Escape the code.
+    final escaped = escapeHtml(childLines.join('\n'));
+
+    return new Element('pre', [new Element.text('code', escaped)]);
+  }
+}
+
 /// Parses horizontal rules like `---`, `_ _ _`, `*  *  *`, etc.
 class HorizontalRuleSyntax extends BlockSyntax {
   RegExp get pattern => _RE_HR;