Fix generation of target in Xcode project when using output_name.

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 25f2415f516887e8279d9f01a842b75c1f2e6723..2ad43cceefc4567abad8d2ca2123794f0c0cf606 100644
--- a/tools/gn/xcode_object.h
+++ b/tools/gn/xcode_object.h
@@ -243,6 +243,7 @@ class PBXNativeTarget : public PBXTarget {
                   const std::string& config_name,
                   const PBXAttributes& attributes,
                   const std::string& product_type,
+                  const std::string& product_name,
                   const PBXFileReference* product_reference);
   ~PBXNativeTarget() override;
 
@@ -255,6 +256,7 @@ class PBXNativeTarget : public PBXTarget {
  private:
   const PBXFileReference* product_reference_;
   std::string product_type_;
+  std::string product_name_;
 
   DISALLOW_COPY_AND_ASSIGN(PBXNativeTarget);
 };