Implement tracking of BUILD.gn files used to define target, toolchain or

tools/gn/item.h

Index: tools/gn/item.h
diff --git a/tools/gn/item.h b/tools/gn/item.h
index 3ec482af1df7b11445f07eee1dcb139f48c28ae9..8ab5a089d964120a59f5bf76b025d5b90999ee3a 100644
--- a/tools/gn/item.h
+++ b/tools/gn/item.h
@@ -5,9 +5,11 @@
 #ifndef TOOLS_GN_ITEM_H_
 #define TOOLS_GN_ITEM_H_
 
+#include <set>
 #include <string>
 
 #include "tools/gn/label.h"
+#include "tools/gn/source_file.h"
 #include "tools/gn/visibility.h"
 
 class Config;
@@ -21,7 +23,9 @@ class Toolchain;
 // graph.
 class Item {
  public:
-  Item(const Settings* settings, const Label& label);
+  Item(const Settings* settings,
+       const Label& label,
+       const std::set<uint32_t>& source_files_hashes);
   virtual ~Item();
 
   const Settings* settings() const { return settings_; }
@@ -55,12 +59,17 @@ class Item {
   // returns false on failure.
   virtual bool OnResolved(Err* err);
 
+  const std::set<uint32_t>& source_files_hashes() const {
+    return source_files_hashes_;
+  }
+
  private:
   const Settings* settings_;
   Label label_;
   const ParseNode* defined_from_;
 
   Visibility visibility_;
+  std::set<uint32_t> source_files_hashes_;
 };
 
 #endif  // TOOLS_GN_ITEM_H_