GN: don't write separate files for non-binary targets

tools/gn/ninja_target_writer.h

 // 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.
 
 #ifndef TOOLS_GN_NINJA_TARGET_WRITER_H_
 #define TOOLS_GN_NINJA_TARGET_WRITER_H_
 
 #include <iosfwd>
 
 #include "base/macros.h"
 #include "tools/gn/path_output.h"
 #include "tools/gn/substitution_type.h"
 
 class FileTemplate;
 class OutputFile;
 class Settings;
 class Target;
 struct SubstitutionBits;
 
 // Generates one target's ".ninja" file. The toplevel "build.ninja" file is
 // generated by the NinjaBuildWriter.
 class NinjaTargetWriter {
  public:
   NinjaTargetWriter(const Target* target, std::ostream& out);
   virtual ~NinjaTargetWriter();
 
-  static void RunAndWriteFile(const Target* target);
+  // Returns the build line to be written to the toolchain build file.
+  //
+  // Some targets have their rules written to separate files, and some can have
+  // their rules coalesced in the main build file. For the coalesced case, this
+  // function will return the rules as a string. For the separate file case,
+  // the separate ninja file will be written and the return string will be the
+  // subninja command to load that file.
+  static std::string RunAndWriteFile(const Target* target);
 
   virtual void Run() = 0;
 
  protected:
   // Writes out the substitution values that are shared between the different
   // types of tools (target gen dir, target label, etc.). Only the substitutions
   // identified by the given bits will be written.
   void WriteSharedVars(const SubstitutionBits& bits);
 
   // Writes to the output stream a stamp rule for input dependencies, and
@@ skipping 16 matching lines @@
   PathOutput path_output_;
 
  private:
   void WriteCopyRules();
   void WriteEscapedSubstitution(SubstitutionType type);
 
   DISALLOW_COPY_AND_ASSIGN(NinjaTargetWriter);
 };
 
 #endif  // TOOLS_GN_NINJA_TARGET_WRITER_H_