GN: Mark variables in nested scopes used for += and -=.

tools/gn/operators.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/operators.h"
 
 #include <stddef.h>
 #include <algorithm>
 
 #include "base/strings/string_number_conversions.h"
@@ skipping 137 matching lines @@
     return false;
   }
   type_ = SCOPE;
   scope_ = base->scope_value();
   name_token_ = &dest_accessor->member()->value();
   return true;
 }
 
 const Value* ValueDestination::GetExistingValue() const {
   if (type_ == SCOPE)
-    return scope_->GetValue(name_token_->value(), false);
+    return scope_->GetValue(name_token_->value(), true);
   else if (type_ == LIST)
     return &list_->list_value()[index_];
   return nullptr;
 }
 
 Value* ValueDestination::GetExistingMutableValueIfExists(
     const ParseNode* origin) {
   if (type_ == SCOPE) {
     Value* value = scope_->GetMutableValue(
         name_token_->value(), Scope::SEARCH_CURRENT, false);
@@ skipping 605 matching lines @@
     return ExecuteGreaterEquals(scope, op_node, left_value, right_value, err);
   if (op.type() == Token::LESS_EQUAL)
     return ExecuteLessEquals(scope, op_node, left_value, right_value, err);
   if (op.type() == Token::GREATER_THAN)
     return ExecuteGreater(scope, op_node, left_value, right_value, err);
   if (op.type() == Token::LESS_THAN)
     return ExecuteLess(scope, op_node, left_value, right_value, err);
 
   return Value();
 }