Remove use of <iostream> where unnecessary.

tools/imagediff/image_diff.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file input format is based loosely on
 // Tools/DumpRenderTree/ImageDiff.m
 
 // The exact format of this tool's output to stdout is important, to match
 // what the run-webkit-tests script expects.
 
 #include <algorithm>
 #include <vector>
 #include <string>
-#include <iostream>
+#include <ostream>
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/process_util.h"
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
@@ skipping 348 matching lines @@
                         FilePath(args[1]),
                         FilePath(args[2]));
     }
   } else if (args.size() == 2) {
     return CompareImages(FilePath(args[0]), FilePath(args[1]));
   }
 
   PrintHelp();
   return kStatusError;
 }