gn: Support build directories outside the source tree.

tools/gn/visibility.cc

Index: tools/gn/visibility.cc
diff --git a/tools/gn/visibility.cc b/tools/gn/visibility.cc
index a61a5cd9c45f7effb57fd053be21ddaf29a6122e..83f0a83bc295eba2d53c533d22ae77885d53b9d4 100644
--- a/tools/gn/visibility.cc
+++ b/tools/gn/visibility.cc
@@ -20,7 +20,8 @@ Visibility::Visibility() {
 Visibility::~Visibility() {
 }
 
-bool Visibility::Set(const SourceDir& current_dir,
+bool Visibility::Set(const base::FilePath& source_root,
+                     const SourceDir& current_dir,
                      const Value& value,
                      Err* err) {
   patterns_.clear();
@@ -31,7 +32,8 @@ bool Visibility::Set(const SourceDir& current_dir,
   }
 
   for (const auto& item : value.list_value()) {
-    patterns_.push_back(LabelPattern::GetPattern(current_dir, item, err));
+    patterns_.push_back(LabelPattern::GetPattern(source_root, current_dir,
+                                                 item, err));
     if (err->has_error())
       return false;
   }
@@ -103,7 +105,8 @@ bool Visibility::CheckItemVisibility(const Item* from,
 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);
+    item->visibility().Set(scope->settings()->build_settings()->root_path(),
+                           scope->GetSourceDir(), *vis_value, err);
   else  // Default to public.
     item->visibility().SetPublic();
   return !err->has_error();