tools/gn: Convert for loops to use the new range-based loops in C++11.

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 "base/strings/string_number_conversions.h"
 #include "tools/gn/err.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
@@ skipping 80 matching lines @@
       }
       if (!found_match) {
         *err = Err(to_remove.origin()->GetRange(), "Item not found",
             "You were trying to remove " + to_remove.ToString(true) +
             "\nfrom the list but it wasn't there.");
       }
       break;
     }
 
     case Value::LIST:  // Filter out each individual thing.
-      for (size_t i = 0; i < to_remove.list_value().size(); i++) {
+      for (const auto& elem : to_remove.list_value()) {
         // TODO(brettw) if the nested item is a list, we may want to search
         // for the literal list rather than remote the items in it.
-        RemoveMatchesFromList(op_node, list, to_remove.list_value()[i], err);
+        RemoveMatchesFromList(op_node, list, elem, err);
         if (err->has_error())
           return;
       }
       break;
 
     default:
       break;
   }
 }
 
@@ skipping 461 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();
 }