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.
@@ skipping 130 matching lines @@
     #        '<(grit_out_dir)/grit/component_extension_resources_map.cc',
     #        '<(grit_out_dir)/grit/theme_resources_map.cc',
     #        '<(SHARED_INTERMEDIATE_DIR)/ui/resources/grit/ui_resources_map.cc',
     #
     #        # This file is generated by
     #        # chrome/browser/metrics/variations/generate_resources_map.py
     #        '<(SHARED_INTERMEDIATE_DIR)/chrome/browser/metrics/variations/generated_resources_map.cc',
 
     defines = nacl_defines
 
+    if (debug_devtools) {
+      defines += [ "DEBUG_DEVTOOLS=1" ]
+    }
+
     deps += [
       "//apps",
       "//cc",
       "//chrome/browser/devtools",
       "//chrome/installer/util",
       "//components/autofill/content/browser",
       "//components/dom_distiller/content",
       "//components/keyed_service/content",
       "//components/navigation_interception",
       "//components/password_manager/content/browser",
@@ skipping 105 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",
     ]
   }
 }