[DevTools] use debug_frontend flag in content_shell for tests

content/shell/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/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//build/config/win/console_app.gni")
 import("//build/config/win/manifest.gni")
 import("//tools/grit/repack.gni")
@@ skipping 158 matching lines @@
     "utility/shell_content_utility_client.cc",
     "utility/shell_content_utility_client.h",
   ]
 
   configs += [
     ":content_shell_lib_warnings",
     "//build/config:precompiled_headers",
 
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
+
+    "//third_party/WebKit/public:debug_devtools",
   ]
 
   defines = [ "CONTENT_SHELL_VERSION=\"$content_shell_version\"" ]
 
   public_deps = [
     # This exposes all public content APIs.
     "//content/public/app:both",
     "//content/public/browser",
     "//content/public/common",
     "//content/public/plugin",
@@ skipping 302 matching lines @@
     sources = [
       "app/shell_content_main.cc",
       "app/shell_content_main.h",
     ]
 
     deps = [
       ":content_shell_lib",
     ]
   }
 }