Remove remaining legacy SplitString calls.

tools/gn/standard_out.cc

 // Copyright (c) 2013 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.
 
 #include "tools/gn/standard_out.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 186 matching lines @@
     OutputString(line.substr(begin_bracket, first_normal - begin_bracket),
                  DECORATION_DIM);
   }
 
   OutputString(line.substr(first_normal) + "\n");
 }
 
 void PrintLongHelp(const std::string& text) {
   EnsureInitialized();
 
-  std::vector<std::string> lines;
-  base::SplitStringDontTrim(text, '\n', &lines);
-
   bool first_header = true;
   bool in_body = false;
-  for (const auto& line : lines) {
+  for (const std::string& line : base::SplitString(
+           text, "\n", base::KEEP_WHITESPACE, base::SPLIT_WANT_ALL)) {
     // Check for a heading line.
     if (!line.empty() && line[0] != ' ') {
       if (is_markdown) {
         // GN's block-level formatting is converted to markdown as follows:
         // * The first heading is treated as an H2.
         // * Subsequent heading are treated as H3s.
         // * Any other text is wrapped in a code block and displayed as-is.
         //
         // Span-level formatting (the decorations) is converted inside
         // OutputString().
@@ skipping 35 matching lines @@
       }
     }
 
     OutputString(line + "\n", dec);
   }
 
   if (is_markdown && in_body)
     OutputString("\n```\n");
 }