Hook up WebKit WTF to GN build.

build/config/clang/clang.gni

Index: build/config/clang/clang.gni
diff --git a/build/config/clang/clang.gni b/build/config/clang/clang.gni
new file mode 100644
index 0000000000000000000000000000000000000000..3b2d76fbe6af7e41ad6d3d309a26fb439f86d8e1
--- /dev/null
+++ b/build/config/clang/clang.gni
@@ -0,0 +1,9 @@
+# Copyright 2014 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.
+
+declare_args() {
+  # Indicates if the build should use the Chrome-specific plugins for enforcing
+  # coding guidelines, etc. Only used when compiling with Clang.
+  clang_use_chrome_plugins = is_clang
+}