Use paths relative to build dir in custom actions.

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"
@@ skipping 76 matching lines @@
     // The build command goes in the rsp file.
     out_ << "  rspfile_content = ";
     path_output_.WriteFile(out_, settings_->build_settings()->python_path());
     out_ << " ";
     path_output_.WriteFile(out_, target_->script_values().script());
     args_template.WriteWithNinjaExpansions(out_);
     out_ << std::endl;
   } else {
     // Posix can execute Python directly.
     out_ << "rule " << custom_rule_name << std::endl;
-    out_ << "  command = cd ";
-    path_output_.WriteDir(out_, target_->label().dir(),
-                          PathOutput::DIR_NO_LAST_SLASH);
-    out_ << "; $pythonpath ";
+    out_ << "  command = ";
+    path_output_.WriteFile(out_, settings_->build_settings()->python_path());
+    out_ << " ";
     path_output_.WriteFile(out_, target_->script_values().script());
     args_template.WriteWithNinjaExpansions(out_);
     out_ << std::endl;
     out_ << "  description = CUSTOM " << target_label << std::endl;
     out_ << "  restat = 1" << std::endl;
   }
 
   out_ << std::endl;
   return custom_rule_name;
 }
@@ skipping 17 matching lines @@
     const std::string& implicit_deps,
     const FileTemplate& args_template,
     std::vector<OutputFile>* output_files) {
   FileTemplate output_template(GetOutputTemplate());
 
   const Target::FileList& sources = target_->sources();
   for (size_t i = 0; i < sources.size(); i++) {
     out_ << "build";
     WriteOutputFilesForBuildLine(output_template, sources[i], output_files);
 
-    out_ << ": " << custom_rule_name;
+    out_ << ": " << custom_rule_name << " ";
     path_output_.WriteFile(out_, sources[i]);
     out_ << implicit_deps << std::endl;
 
     // Windows needs a unique ID for the response file.
     if (target_->settings()->IsWin())
       out_ << "  unique_name = " << i << std::endl;
 
     if (args_template.has_substitutions())
       WriteArgsSubstitutions(sources[i], args_template);
   }
@@ skipping 19 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);
   }
 }