Add initial prototype for the GN meta-buildsystem.

tools/gn/ninja_target_writer.h

Index: tools/gn/ninja_target_writer.h
diff --git a/tools/gn/ninja_target_writer.h b/tools/gn/ninja_target_writer.h
new file mode 100644
index 0000000000000000000000000000000000000000..5e6827d550950e990c31fa859537d7b0265edfa1
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+++ b/tools/gn/ninja_target_writer.h
@@ -0,0 +1,67 @@
+// 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 <string>
+
+#include "base/basictypes.h"
+#include "base/files/file_path.h"
+#include "tools/gn/filesystem_utils.h"
+#include "tools/gn/ninja_helper.h"
+#include "tools/gn/path_output.h"
+#include "tools/gn/settings.h"
+
+class Target;
+
+// Generates one target's ".ninja" file. The toplevel "build.ninja" file is
+// generated by the NinjaBuildGenerator.
+class NinjaTargetWriter {
+ public:
+  NinjaTargetWriter(const Target* target, std::ostream& out);
+  ~NinjaTargetWriter();
+
+  void Run();
+
+  static void RunAndWriteFile(const Target* target);
+
+ private:
+  void WriteCopyRules();
+
+  void WriteCustomRules();
+  void WriteCustomArg(const std::string& arg);
+
+  // Writs the rules for compiling each source, writing all output files
+  // to the given vector.
+  //
+  // common_deps is a precomputed string of all ninja files that are common
+  // to each build step. This is added to each one.
+  void WriteCustomSourceRules(const std::string& custom_rule_name,
+                              const std::string& common_deps,
+                              const SourceDir& script_cd,
+                              const std::string& script_cd_to_root,
+                              std::vector<OutputFile>* output_files);
+
+  void WriteCompilerVars();
+  void WriteSources(std::vector<OutputFile>* object_files);
+  void WriteLinkerStuff(const std::vector<OutputFile>& object_files);
+
+  // Returns NULL if the source type should not be compiled on this target.
+  const char* GetCommandForSourceType(SourceFileType type) const;
+
+  const char* GetCommandForTargetType() const;
+
+  const Settings* settings_;  // Non-owning.
+  const Target* target_;  // Non-owning.
+  std::ostream& out_;
+  PathOutput path_output_;
+
+  NinjaHelper helper_;
+
+  DISALLOW_COPY_AND_ASSIGN(NinjaTargetWriter);
+};
+
+#endif  // TOOLS_GN_NINJA_TARGET_WRITER_H_