Move debug_devtools to a buildflag_header.

third_party/WebKit/public/public_features.gni

Index: third_party/WebKit/public/public_features.gni
diff --git a/third_party/WebKit/public/public_features.gni b/third_party/WebKit/public/public_features.gni
new file mode 100644
index 0000000000000000000000000000000000000000..6d2e3731ed1d73aee7e293cc44f207eedbbf0869
--- /dev/null
+++ b/third_party/WebKit/public/public_features.gni
@@ -0,0 +1,11 @@
+# Copyright 2016 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() {
+  # If debug_devtools is set to true, JavaScript files for DevTools are stored
+  # as is and loaded from disk. Otherwise, a concatenated file is stored in
+  # resources.pak. It is still possible to load JS files from disk by passing
+  # --debug-devtools cmdline switch.
+  debug_devtools = false
+}