[Refactor Xcode Objects] Enable generating per file '--help' compiler flag

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..03f804a4bf637998a0a20f67baf64b054a99ee22 100644
--- a/tools/gn/xcode_object.h
+++ b/tools/gn/xcode_object.h
@@ -153,8 +153,11 @@ class PBXAggregateTarget : public PBXTarget {
 
 class PBXBuildFile : public PBXObject {
  public:
+  enum HelpCompilerFlagEnabled { HELP_FLAG_ENABLED, HELP_FLAG_DISABLED };
+
   PBXBuildFile(const PBXFileReference* file_reference,
-               const PBXSourcesBuildPhase* build_phase);
+               const PBXSourcesBuildPhase* build_phase,
+               const HelpCompilerFlagEnabled help_flag_enabled);
   ~PBXBuildFile() override;
 
   // PXBObject implementation.
@@ -165,6 +168,7 @@ class PBXBuildFile : public PBXObject {
  private:
   const PBXFileReference* file_reference_;
   const PBXSourcesBuildPhase* build_phase_;
+  const HelpCompilerFlagEnabled help_flag_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(PBXBuildFile);
 };
@@ -247,7 +251,8 @@ class PBXNativeTarget : public PBXTarget {
                   const PBXFileReference* product_reference);
   ~PBXNativeTarget() override;
 
-  void AddFileForIndexing(const PBXFileReference* file_reference);
+  void AddFileForIndexing(const PBXFileReference* file_reference,
+                          const PBXBuildFile::HelpCompilerFlagEnabled);
 
   // PBXObject implementation.
   PBXObjectClass Class() const override;
@@ -271,7 +276,10 @@ class PBXProject : public PBXObject {
              const PBXAttributes& attributes);
   ~PBXProject() override;
 
-  void AddSourceFile(const std::string& source_path);
+  void AddSourceFile(
+      const std::string& source_path,
+      const PBXBuildFile::HelpCompilerFlagEnabled help_flag_enabled =
+          PBXBuildFile::HelpCompilerFlagEnabled::HELP_FLAG_DISABLED);
   void AddAggregateTarget(const std::string& name,
                           const std::string& shell_script);
   void AddNativeTarget(const std::string& name,