Add GN variables for controlling header checking.

tools/gn/target.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/target.h"
 
 #include "base/bind.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "tools/gn/config_values_extractors.h"
@@ skipping 27 matching lines @@
     dest->push_back(all[i]);
   }
 }
 
 }  // namespace
 
 Target::Target(const Settings* settings, const Label& label)
     : Item(settings, label),
       output_type_(UNKNOWN),
       all_headers_public_(true),
+      check_includes_(true),
       hard_dep_(false),
       toolchain_(NULL) {
 }
 
 Target::~Target() {
 }
 
 // static
 const char* Target::GetStringForOutputType(OutputType type) {
   switch (type) {
@@ skipping 240 matching lines @@
               SubstitutionWriter::ApplyPatternToLinkerAsOutputFile(
                   this, tool, tool->link_output());
         }
       }
       break;
     case UNKNOWN:
     default:
       NOTREACHED();
   }
 }