[Refactor Xcode Objects] Decouple file references and indexing target.

tools/gn/xcode_object.h

Index: tools/gn/xcode_object.h
diff --git a/tools/gn/xcode_object.h b/tools/gn/xcode_object.h
index 2ad43cceefc4567abad8d2ca2123794f0c0cf606..74a37fa98ca6c3beb296a3340a5c28750077874c 100644
--- a/tools/gn/xcode_object.h
+++ b/tools/gn/xcode_object.h
@@ -271,14 +271,17 @@ class PBXProject : public PBXObject {
              const PBXAttributes& attributes);
   ~PBXProject() override;
 
-  void AddSourceFile(const std::string& source_path);
+  void AddSourceFileToIndexingTarget(const std::string& source_path);
+  void AddSourceFile(const std::string& source_path, PBXNativeTarget* target);
+
   void AddAggregateTarget(const std::string& name,
                           const std::string& shell_script);
-  void AddNativeTarget(const std::string& name,
-                       const std::string& type,
-                       const std::string& output_name,
-                       const std::string& output_type,
-                       const std::string& shell_script);
+  void AddIndexingTarget();
+  PBXNativeTarget* AddNativeTarget(const std::string& name,

[sdefresne, 2016/12/16 23:51:55]

Why do you change the return value of this method? Is this for a followup CL? I
do not see any change to the caller of that method, so the returned value is
unused in that CL. Can you move the change to the followup CL instead and revert
in this one (or point me to where the value is used, I may have missed it).

[liaoyuke, 2016/12/19 08:03:35]

Done. Yes, it is for a followup CL, I will move the change to later.

+                                   const std::string& type,
+                                   const std::string& output_name,
+                                   const std::string& output_type,
+                                   const std::string& shell_script);
 
   void SetProjectDirPath(const std::string& project_dir_path);
   void SetProjectRoot(const std::string& project_root);