Fix and test for leading comment handling (dartbug.com/15876).

pkg/analyzer/lib/src/services/formatter_impl.dart

 // Copyright (c) 2013, 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.
 
 library formatter_impl;
 
 import 'dart:math';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/java_core.dart' show CharSequence;
@@ skipping 1479 matching lines @@
   int emitPrecedingCommentsAndNewlines(Token token, {min: 0}) {
 
     var comment = token.precedingComments;
     var currentToken = comment != null ? comment : token;
 
     //Handle EOLs before newlines
     if (isAtEOL(comment)) {
       emitComment(comment, previousToken);
       comment = comment.next;
       currentToken = comment != null ? comment : token;
+      // Ensure EOL comments force a linebreak
+      needsNewline = true;
     }
 
     var lines = 0;
     if (needsNewline || preserveNewlines) {
       lines = max(min, countNewlinesBetween(previousToken, currentToken));
       preserveNewlines = false;
     }
     emitNewlines(lines);
 
     previousToken =
@@ skipping 116 matching lines @@
     var lastLine =
         lineInfo.getLocation(lastOffset).lineNumber;
     var currentLine =
         lineInfo.getLocation(currentOffset).lineNumber;
     return currentLine - lastLine;
   }
 
   String toString() => writer.toString();
 
 }