Add not_needed function

tools/gn/scope.h

Index: tools/gn/scope.h
diff --git a/tools/gn/scope.h b/tools/gn/scope.h
index 31bac6261464826a3bd069b3dd7d87ba5f5eaeba..579947afbc3c88e1f61dc5f96da65954f7f5674f 100644
--- a/tools/gn/scope.h
+++ b/tools/gn/scope.h
@@ -204,10 +204,14 @@ class Scope {
   const Template* GetTemplate(const std::string& name) const;
 
   // Marks the given identifier as (un)used in the current scope.
-  void MarkUsed(const base::StringPiece& ident);
-  void MarkAllUsed();
+  void MarkUsed(const base::StringPiece& ident, Err* err);
+  void MarkAllUsed(Err* err);
   void MarkUnused(const base::StringPiece& ident);
 
+  // Marks the given identifier as unusable in the current scope.
+  void MarkAllUnusable(Err* err, std::set<std::string> excluded_values);

[brettw, 2017/06/20 17:27:25]

The set should be passed by const ref.

[Petr Hosek, 2017/06/21 02:17:40]

Done.

+  void MarkUnusable(const base::StringPiece& ident, Err* err);
+
   // Checks to see if the scope has a var set that hasn't been used. This is
   // called before replacing the var with a different one. It does not check
   // containing scopes.
@@ -320,10 +324,11 @@ class Scope {
   friend class ProgrammaticProvider;
 
   struct Record {
-    Record() : used(false) {}
-    explicit Record(const Value& v) : used(false), value(v) {}
+    Record() : used(false), unusable(false) {}
+    explicit Record(const Value& v) : used(false), unusable(false), value(v) {}
 
     bool used;  // Set to true when the variable is used.
+    bool unusable;
     Value value;
   };