Handle the "debug_devtools" build arg in GN builds

chrome/browser/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("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//components/nacl/nacl_defines.gni")
 # //build/config/android/rules.gni imports //tools/grit/grit_rule.gni, which
 # produces a conflict for the "grit" template so we have to only include one.
 if (is_android) {
   import("//build/config/android/rules.gni")
 } else {
   import("//tools/grit/grit_rule.gni")
 }
 
 about_credits_file = "$target_gen_dir/about_credits.html"
 additional_modules_list_file =
     "$root_gen_dir/chrome/browser/internal/additional_modules_list.txt"
 
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
     [ rebase_path("../chrome_browser.gypi") ],
     "scope",
     [ "../chrome_browser.gypi" ])
 
 static_library("browser") {
-  configs += [ "//build/config/compiler:wexit_time_destructors" ]
+  configs += [
+    "//build/config/compiler:wexit_time_destructors",
+    "//third_party/WebKit/public:debug_devtools",
+  ]
   defines = []
   sources = []
   libs = []
   ldflags = []
 
   # iOS/non-iOS shared deps. New dependencies should generally be added in the
   # non-iOS deps below.
   public_deps = [
     "//components/autofill/core/browser",
     "//content/public/browser",
@@ skipping 227 matching lines @@
   if (enable_spellcheck) {
     sources += rebase_path(gypi_values.chrome_browser_spellchecker_sources,
                            ".", "//chrome")
     deps += [ "//third_party/hunspell" ]
   }
   if (enable_nacl) {
     sources += rebase_path(gypi_values.chrome_browser_nacl_sources,
                            ".", "//chrome")
     #deps += [ "//components/nacl:nacl_browser" ]  TODO(GYP)
   }
-  # ["debug_devtools==1", {  TODO(GYP)
-  #   "defines": [
-  #     "DEBUG_DEVTOOLS=1",
-  # }],
+
   if (enable_configuration_policy) {
     sources += rebase_path(
         gypi_values.chrome_browser_policy_shared_with_ios_sources,
         ".", "//chrome")
     deps += [
       "//components/policy",
       "//components/policy/proto",
     ]
     if (!is_ios) {
       sources += rebase_path(
@@ skipping 634 matching lines @@
     ]
   }
 
   if (enable_wifi_bootstrapping) {
     sources += [
       "local_discovery/wifi/mock_wifi_manager.cc",
       "local_discovery/wifi/mock_wifi_manager.h",
     ]
   }
 }