Add not_needed function

tools/gn/scope.cc

 // Copyright (c) 2013 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/scope.h"
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/template.h"
@@ skipping 201 matching lines @@
     return;
   }
   found->second.used = true;
 }
 
 void Scope::MarkAllUsed() {
   for (auto& cur : values_)
     cur.second.used = true;
 }
 
+void Scope::MarkAllUsed(const std::set<std::string>& excluded_values) {
+  for (auto& cur : values_) {
+    if (!excluded_values.empty() &&
+        excluded_values.find(cur.first.as_string()) != excluded_values.end()) {
+      continue;  // Skip this excluded value.
+    }
+    cur.second.used = true;
+  }
+}
+
 void Scope::MarkUnused(const base::StringPiece& ident) {
   RecordMap::iterator found = values_.find(ident);
   if (found == values_.end()) {
     NOTREACHED();
     return;
   }
   found->second.used = false;
 }
 
 bool Scope::IsSetButUnused(const base::StringPiece& ident) const {
@@ skipping 307 matching lines @@
     return false;
   for (const auto& pair : a) {
     const auto& found_b = b.find(pair.first);
     if (found_b == b.end())
       return false;  // Item in 'a' but not 'b'.
     if (pair.second.value != found_b->second.value)
       return false;  // Values for variable in 'a' and 'b' are different.
   }
   return true;
 }