[Refactor Xcode Objects] Allow extra attributes for native targets.

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 f56de09a7806658b2cf4c870be1fddc332e6bdd5..12f268f86bbdfc9bada5fffb2e5b0fe7c26cc2ee 100644
--- a/tools/gn/xcode_object.h
+++ b/tools/gn/xcode_object.h
@@ -284,11 +284,14 @@ class PBXProject : public PBXObject {
   void AddAggregateTarget(const std::string& name,
                           const std::string& shell_script);
   void AddIndexingTarget();
+
+  // NOTE: |extra_attributes| values may be overridden within this function.

[sdefresne, 2016/12/21 09:39:12]

I understand what you mean by this comment, but only after reading the code.
I've tried to think of better comments (things like "Attributes from
|extra_attributes| may be ignored.") but nothing that meant the code clearer to
understand. In fact, I find it easier to understand without the comment (as I
then think "oh, they are extra attributes, so I can only set things that are not
already set inside the function).

WDYT about just removing this comment?

[liaoyuke, 2016/12/21 16:59:26]

Make sense. The "extra" in the name should explain everything.

   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);
+                       const std::string& shell_script,
+                       const PBXAttributes& extra_attributes = PBXAttributes());
 
   void SetProjectDirPath(const std::string& project_dir_path);
   void SetProjectRoot(const std::string& project_root);