Improve Windows GN build setup.

tools/gn/ninja_script_target_writer.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/ninja_script_target_writer.h"
 
 #include "base/strings/string_util.h"
 #include "tools/gn/err.h"
 #include "tools/gn/file_template.h"
 #include "tools/gn/string_utils.h"
 #include "tools/gn/target.h"
 
 NinjaScriptTargetWriter::NinjaScriptTargetWriter(const Target* target,
                                                  std::ostream& out)
     : NinjaTargetWriter(target, out),
       path_output_no_escaping_(
           target->settings()->build_settings()->build_dir(),
           ESCAPE_NONE, false) {
 }
 
 NinjaScriptTargetWriter::~NinjaScriptTargetWriter() {
 }
 
 void NinjaScriptTargetWriter::Run() {
-  WriteEnvironment();
-
   FileTemplate args_template(target_->script_values().args());
   std::string custom_rule_name = WriteRuleDefinition(args_template);
   std::string implicit_deps = GetSourcesImplicitDeps();
 
   // Collects all output files for writing below.
   std::vector<OutputFile> output_files;
 
   if (has_sources()) {
     // Write separate build lines for each input source file.
     WriteSourceRules(custom_rule_name, implicit_deps, args_template,
@@ skipping 129 matching lines @@
     std::vector<OutputFile>* output_files) {
   std::vector<std::string> output_template_result;
   output_template.ApplyString(source.value(), &output_template_result);
   for (size_t out_i = 0; out_i < output_template_result.size(); out_i++) {
     OutputFile output_path(output_template_result[out_i]);
     output_files->push_back(output_path);
     out_ << " ";
     path_output_.WriteFile(out_, output_path);
   }
 }