Add the concept of a source set to GN.

tools/gn/ninja_binary_target_writer.h

Index: tools/gn/ninja_binary_target_writer.h
diff --git a/tools/gn/ninja_binary_target_writer.h b/tools/gn/ninja_binary_target_writer.h
index 047ed2a46cd2f272dad8fe5848615a8d4d2aa4b8..8c57ffb2743bf3921f58eadc7811808888044998 100644
--- a/tools/gn/ninja_binary_target_writer.h
+++ b/tools/gn/ninja_binary_target_writer.h
@@ -19,6 +19,8 @@ class NinjaBinaryTargetWriter : public NinjaTargetWriter {
   virtual void Run() OVERRIDE;
 
  private:
+  typedef std::set<OutputFile> OutputFileSet;
+
   void WriteCompilerVars();
   void WriteSources(std::vector<OutputFile>* object_files);
   void WriteLinkerStuff(const std::vector<OutputFile>& object_files);
@@ -29,6 +31,32 @@ class NinjaBinaryTargetWriter : public NinjaTargetWriter {
                         const OutputFile& internal_output_file,
                         const std::vector<OutputFile>& object_files);
 
+  // Writes the stamp line for a source set. These are not linked.
+  void WriteSourceSetStamp(const std::vector<OutputFile>& object_files);
+
+  // Gets all target dependencies and classifies them, as well as accumulates
+  // object files from source sets we need to link.
+  void GetDeps(std::set<OutputFile>* extra_object_files,
+               std::vector<const Target*>* linkable_deps,
+               std::vector<const Target*>* non_linkable_deps) const;
+
+  // Classifies the dependency as linkable or nonlinkable with the current
+  // target, adding it to the appropriate vector. If the dependency is a source
+  // set we should link in, the source set's object files will be appended to
+  // |extra_object_files|.
+  void ClassifyDependency(const Target* dep,
+                          std::set<OutputFile>* extra_object_files,
+                          std::vector<const Target*>* linkable_deps,
+                          std::vector<const Target*>* non_linkable_deps) const;
+
+  // Writes the implicit dependencies for the link or stamp line. This is
+  // the "||" and everything following it on the ninja line.
+  //
+  // The implicit dependencies are the non-linkable deps passed in as an
+  // argument, plus the data file depdencies in the target.
+  void WriteImplicitDependencies(
+      const std::vector<const Target*>& non_linkable_deps);
+
   Toolchain::ToolType tool_type_;
 
   DISALLOW_COPY_AND_ASSIGN(NinjaBinaryTargetWriter);