Add forward_variables_from() and target() to GN

tools/gn/scope_unittest.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 "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/input_file.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/template.h"
 #include "tools/gn/test_with_scope.h"
@@ skipping 161 matching lines @@
 
     Err err;
     Scope::MergeOptions options;
     EXPECT_TRUE(setup.scope()->NonRecursiveMergeTo(
         &new_scope, options, &assignment, "error", &err));
     EXPECT_FALSE(err.has_error());
     EXPECT_FALSE(new_scope.CheckForUnusedVars(&err));
     EXPECT_TRUE(err.has_error());
   }
 
-  // Mark used.
+  // Mark dest used.
   {
     Scope new_scope(setup.settings());
 
     Err err;
     Scope::MergeOptions options;
-    options.mark_used = true;
+    options.mark_dest_used = true;
     EXPECT_TRUE(setup.scope()->NonRecursiveMergeTo(
         &new_scope, options, &assignment, "error", &err));
     EXPECT_FALSE(err.has_error());
     EXPECT_TRUE(new_scope.CheckForUnusedVars(&err));
     EXPECT_FALSE(err.has_error());
   }
 }
 
 TEST(Scope, MakeClosure) {
   // Create 3 nested scopes [const root from setup] <- nested1 <- nested2.
@@ skipping 87 matching lines @@
 
 TEST(Scope, RemovePrivateIdentifiers) {
   TestWithScope setup;
   setup.scope()->SetValue("a", Value(nullptr, true), nullptr);
   setup.scope()->SetValue("_b", Value(nullptr, true), nullptr);
 
   setup.scope()->RemovePrivateIdentifiers();
   EXPECT_TRUE(setup.scope()->GetValue("a"));
   EXPECT_FALSE(setup.scope()->GetValue("_b"));
 }