Fix for triple-slash dartdocs

sdk/lib/_internal/dartdoc/lib/src/dartdoc/comment_map.dart

 // Copyright (c) 2012, 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.
 
 part of dartdoc;
 
 /**
  * The cached lookup-table to associate doc comments with spans. The outer map
  * is from filenames to doc comments in that file. The inner map maps from the
  * token positions to doc comments. Each position is the starting offset of the
@@ skipping 60 matching lines @@
         if (text.startsWith('/**')) {
           // Remember that we've encountered a doc comment.
           lastComment = stripComment(token.slowToString());
         } else if (text.startsWith('///')) {
           var line = text.substring(3);
           // Allow a leading space.
           if (line.startsWith(' ')) line = line.substring(1);
           if (lastComment == null) {
             lastComment = line;
           } else {
-            lastComment = '$lastComment$line';
+            lastComment = '$lastComment\n$line';
           }
         }
       } else if (token.kind == dart2js.HASH_TOKEN) {
         // Look for `library` to find the library comment.
         final next = token.next;
         if ((lastComment != null) && (next.stringValue == 'library')) {
           _libraryComments[source.sourceUri.toString()] = lastComment;
           lastComment = null;
         }
       } else if (lastComment != null) {
@@ skipping 28 matching lines @@
         line = line.substring(1);
       }
 
       buf.add(line);
       buf.add('\n');
     }
 
     return buf.toString();
   }
 }