Output webkit_version.h into the target_gen_dir.

build/util/BUILD.gn

 # 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.
 
 action("webkit_version") {
   script = "version.py"
 
   lastchange_file = "LASTCHANGE.blink"
 
   template_file = "webkit_version.h.in"
   inputs = [
     lastchange_file,
     template_file,
   ]
 
-  output_file = "$root_gen_dir/webkit_version.h"
+  output_file = "$target_gen_dir/webkit_version.h"
   outputs = [
     output_file,
   ]
 
   args = [
     "-f",
     rebase_path(lastchange_file, root_build_dir),
     rebase_path(template_file, root_build_dir),
     rebase_path(output_file, root_build_dir),
   ]
@@ skipping 11 matching lines @@
   ]
   args = [
     "--file",
     rebase_path(_chrome_version_path, root_build_dir),
     "--template",
     "{\"full-quoted\": \"\\\"@MAJOR@.@MINOR@.@BUILD@.@PATCH@\\\"\"}",
     "--output",
     rebase_path(_output_file, root_build_dir),
   ]
 }