Modify apidoc to prefer handwritten HTML5 docs over those in MDN or generated code.

lib/dartdoc/dartdoc.dart

Index: lib/dartdoc/dartdoc.dart
diff --git a/lib/dartdoc/dartdoc.dart b/lib/dartdoc/dartdoc.dart
index bc510b17e3cbde9e79c3097f68342cda9f823bc3..e08c76b7484ecfd4850d1b2c2943ae63c3ba9143 100644
--- a/lib/dartdoc/dartdoc.dart
+++ b/lib/dartdoc/dartdoc.dart
@@ -636,10 +636,9 @@ class Dartdoc {
     writeln('<h2><strong>${library.name}</strong> library</h2>');
 
     // Look for a comment for the entire library.
-    final comment = _comments.findLibrary(library.baseSource);
+    final comment = getLibraryComment(library);
     if (comment != null) {
-      final html = md.markdownToHtml(comment);
-      writeln('<div class="doc">$html</div>');
+      writeln('<div class="doc">$comment</div>');
     }
 
     // Document the top-level members.
@@ -1053,6 +1052,17 @@ class Dartdoc {
     writeln('</div>');
   }
 
+
+  /** Get the doc comment associated with the given library. */
+  String getLibraryComment(Library library) {
+    // Look for a comment for the entire library.
+    final comment = _comments.findLibrary(library.baseSource);
+    if (comment != null) {
+      return md.markdownToHtml(comment);
+    }
+    return null;
+  }
+
   /** Get the doc comment associated with the given type. */
   String getTypeComment(Type type) {
     String comment = _comments.find(type.span);