GN: toolchain threading cleanup

tools/gn/item.h

Index: tools/gn/item.h
diff --git a/tools/gn/item.h b/tools/gn/item.h
index 2538c50a722cffea66a423c9e81e21b6b8bf778c..69115bd7b3e664dd67352834f0daded786d53f67 100644
--- a/tools/gn/item.h
+++ b/tools/gn/item.h
@@ -11,6 +11,7 @@
 
 class Config;
 class ItemNode;
+class Settings;
 class Target;
 class Toolchain;
 
@@ -18,9 +19,11 @@ class Toolchain;
 // graph.
 class Item {
  public:
-  Item(const Label& label);
+  Item(const Settings* settings, const Label& label);
   virtual ~Item();
 
+  const Settings* settings() const { return settings_; }
+
   // This is guaranteed to never change after construction so this can be
   // accessed from any thread with no locking once the item is constructed.
   const Label& label() const { return label_; }
@@ -49,6 +52,7 @@ class Item {
   virtual void OnResolved() {}
 
  private:
+  const Settings* settings_;
   Label label_;
 
   ItemNode* item_node_;