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

This CL refactors xcode objects to allow specifying extra attributes for native
targets, which enables configuring the build settings.

BUG=614818

Review-Url: https://codereview.chromium.org/2591893002
Cr-Commit-Position: refs/heads/master@{#440184}

tools/gn/xcode_object.cc

@@ -679,7 +679,8 @@ void PBXProject::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) {
   base::StringPiece ext = FindExtension(&output_name);
   PBXFileReference* product = static_cast<PBXFileReference*>(
       products_->AddChild(base::MakeUnique<PBXFileReference>(
@@ -691,7 +692,7 @@ void PBXProject::AddNativeTarget(const std::string& name,
                                  ? output_name.substr(0, ext_offset - 1)
                                  : output_name;
 
-  PBXAttributes attributes;
+  PBXAttributes attributes = extra_attributes;
   attributes["CODE_SIGNING_REQUIRED"] = "NO";
   attributes["CONFIGURATION_BUILD_DIR"] = ".";
   attributes["PRODUCT_NAME"] = product_name;

tools/gn/xcode_object.h

@@ -297,7 +297,8 @@ class PBXProject : public PBXObject {
                        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);