Fix GN action target writing with no sources list.

tools/gn/substitution_writer.h

 // Copyright 2014 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.
 
 #ifndef TOOLS_GN_SUBSTITUTION_WRITER_H_
 #define TOOLS_GN_SUBSTITUTION_WRITER_H_
 
 #include <iosfwd>
 #include <vector>
 
@@ skipping 15 matching lines @@
 class SubstitutionWriter {
  public:
   enum OutputStyle {
     OUTPUT_ABSOLUTE,  // Dirs will be absolute "//foo/bar".
     OUTPUT_RELATIVE,  // Dirs will be relative to a given directory.
   };
 
   SubstitutionWriter();
   ~SubstitutionWriter();
 
+  // Converts the given SubstitutionList to OutputFiles assuming there are
+  // no substitutions (it will assert if there are). This is used for cases
+  // like actions where the outputs are explicit, but the list is stored as
+  // a SubstitutionList.
+  static void GetListAsSourceFiles(
+      const Settings* settings,
+      const SubstitutionList& list,
+      std::vector<SourceFile>* output);
+  static void GetListAsOutputFiles(
+      const Settings* settings,
+      const SubstitutionList& list,
+      std::vector<OutputFile>* output);
+
   // Applies the substitution pattern to a source file, returning the result
   // as either a SourceFile or OutputFile.
   static SourceFile ApplyPatternToSource(
       const Settings* settings,
       const SubstitutionPattern& pattern,
       const SourceFile& source);
   static OutputFile ApplyPatternToSourceAsOutputFile(
       const Settings* settings,
       const SubstitutionPattern& pattern,
       const SourceFile& source);
@@ skipping 52 matching lines @@
   // to, otherwise it is ignored.
   static std::string GetSourceSubstitution(
       const Settings* settings,
       const SourceFile& source,
       SubstitutionType type,
       OutputStyle output_style,
       const SourceDir& relative_to);
 };
 
 #endif  // TOOLS_GN_SUBSTITUTION_WRITER_H_