gn: Support build directories outside the source tree.

tools/gn/ninja_action_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_action_target_writer.h"
 
 #include "base/strings/string_util.h"
 #include "tools/gn/deps_iterator.h"
 #include "tools/gn/err.h"
 #include "tools/gn/settings.h"
 #include "tools/gn/string_utils.h"
 #include "tools/gn/substitution_writer.h"
 #include "tools/gn/target.h"
 
 NinjaActionTargetWriter::NinjaActionTargetWriter(const Target* target,
                                                  std::ostream& out)
     : NinjaTargetWriter(target, out),
       path_output_no_escaping_(
           target->settings()->build_settings()->build_dir(),
+          target->settings()->build_settings()->root_path(),
           ESCAPE_NONE) {
 }
 
 NinjaActionTargetWriter::~NinjaActionTargetWriter() {
 }
 
 void NinjaActionTargetWriter::Run() {
   std::string custom_rule_name = WriteRuleDefinition();
 
   // Collect our deps to pass as "extra hard dependencies" for input deps. This
@@ skipping 178 matching lines @@
     out_ << " ";
     path_output_.WriteFile(out_, (*output_files)[i]);
   }
 }
 
 void NinjaActionTargetWriter::WriteDepfile(const SourceFile& source) {
   path_output_.WriteFile(out_,
       SubstitutionWriter::ApplyPatternToSourceAsOutputFile(
           settings_, target_->action_values().depfile(), source));
 }