Improve GN public header file checking

tools/gn/visibility.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/visibility.h"
 
 #include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "tools/gn/err.h"
 #include "tools/gn/filesystem_utils.h"
@@ skipping 60 matching lines @@
   const std::vector<Value>& list = value.list_value();
   for (size_t i = 0; i < list.size(); i++) {
     patterns_.push_back(GetPattern(current_dir, list[i], err));
     if (err->has_error())
       return false;
   }
   return true;
 }
 
 void Visibility::SetPublic() {
+  patterns_.clear();
   patterns_.push_back(
       VisPattern(VisPattern::RECURSIVE_DIRECTORY, SourceDir(), std::string()));
 }
 
 void Visibility::SetPrivate(const SourceDir& current_dir) {
+  patterns_.clear();
   patterns_.push_back(
       VisPattern(VisPattern::DIRECTORY, current_dir, std::string()));
 }
 
 bool Visibility::CanSeeMe(const Label& label) const {
   for (size_t i = 0; i < patterns_.size(); i++) {
     if (patterns_[i].Matches(label))
       return true;
   }
   return false;
@@ skipping 154 matching lines @@
 
 // static
 bool Visibility::FillItemVisibility(Item* item, Scope* scope, Err* err) {
   const Value* vis_value = scope->GetValue(variables::kVisibility, true);
   if (vis_value)
     item->visibility().Set(scope->GetSourceDir(), *vis_value, err);
   else  // Default to public.
     item->visibility().SetPublic();
   return !err->has_error();
 }