DevTools: Support debug_devtools=true arg in GN builds

public/BUILD.gn

 # 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.
 
 import("//tools/grit/grit_rule.gni")
 
 # GYP version: WebKit/public/blink.gyp:blink
 group("blink") {
   deps = [
     ":blink_headers",
@@ skipping 34 matching lines @@
     "//third_party/WebKit/Source/platform:platform_unittests",
     "//third_party/WebKit/Source/web",
     "//third_party/WebKit/Source/wtf:wtf_unittests",
   ]
 }
 
 config("blink_headers_config") {
   include_dirs = [ ".." ]
 }
 
+config("debug_devtools") {
+  if (debug_devtools) {
+    defines = [ "DEBUG_DEVTOOLS=1" ]
+  }
+}
+
 # Depend on this target to use public blink API headers for things like enums
 # and public structures without actually linking against any Blink libraries.
 source_set("blink_headers") {
   public_configs = [
     ":blink_headers_config",
     # Blink exposes icu headers in the public API.
     "//third_party/icu:icu_config",
     # Blink exposes NPAPI headers in the public API.
     "//third_party/npapi:npapi_config",
   ]
@@ skipping 17 matching lines @@
 grit("resources") {
   output_dir = "$root_gen_dir/blink/public/resources"
   use_qualified_include = true
   source = "blink_resources.grd"
   outputs = [
     "grit/blink_resources.h",
     "blink_resources.rc",
     "blink_resources.pak",
   ]
 }