Fix GN action target writing with no sources list.

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/err.h"
 #include "tools/gn/string_utils.h"
 #include "tools/gn/substitution_writer.h"
@@ skipping 35 matching lines @@
   // Collects all output files for writing below.
   std::vector<OutputFile> output_files;
 
   if (target_->output_type() == Target::ACTION_FOREACH) {
     // Write separate build lines for each input source file.
     WriteSourceRules(custom_rule_name, implicit_deps, &output_files);
   } else {
     DCHECK(target_->output_type() == Target::ACTION);
 
     // Write a rule that invokes the script once with the outputs as outputs,
-    // and the data as inputs.
+    // and the data as inputs. It does not depend on the sources.
     out_ << "build";
-    SubstitutionWriter::ApplyListToSourcesAsOutputFile(
-        settings_, target_->action_values().outputs(), target_->sources(),
-        &output_files);
+    SubstitutionWriter::GetListAsOutputFiles(
+        settings_, target_->action_values().outputs(), &output_files);
     for (size_t i = 0; i < output_files.size(); i++) {
       out_ << " ";
       path_output_.WriteFile(out_, output_files[i]);
     }
 
     out_ << ": " << custom_rule_name << implicit_deps << std::endl;
     if (target_->action_values().has_depfile()) {
       out_ << "  depfile = ";
       WriteDepfile(SourceFile());
       out_ << std::endl;
@@ skipping 145 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));
 }