WebUI: disable optimizations (vulcanize) in debug builds

chrome/common/features.gni

 # Copyright 2015 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/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/features.gni")
 import("//extensions/features/features.gni")
 import("//media/media_options.gni")
@@ skipping 47 matching lines @@
 
   # Enables vr shell UI development on local or remote page.
   enable_vr_shell_ui_dev = false
 
   # Enable native notifications via XPC services (mac only).
   enable_xpc_notifications = false
 
   # Indicates if the build is using PGO.
   pgo_build = chrome_pgo_phase > 0
 
-  # Use vulcanized HTML/CSS/JS resources to speed up WebUI (chrome://)
-  # pages. https://github.com/polymer/vulcanize
-  use_vulcanize = true
+  # Optimize parts of Chrome's UI written with web technologies (HTML/CSS/JS)
+  # for runtime performance purposes. This does more work at compile time for
+  # speed benefits at runtime (so we skip in debug builds). TODO(dbeam): rename
+  # this flag "optimize_web_uis" because we run more than vulcanize these days.
+  use_vulcanize = !is_debug
 }
 
 # Use brlapi from brltty for braille display support.
 use_brlapi = is_chromeos
 
 _enable_printing = enable_basic_printing || enable_print_preview
 
 # Every grit target in //chrome should apply these defines so that the
 # proper build flags can be set.
 chrome_grit_defines = [
   "enable_app_list=$enable_app_list",
   "enable_background=$enable_background",
   "enable_extensions=$enable_extensions",
   "enable_google_now=$enable_google_now",
   "enable_hangout_services_extension=$enable_hangout_services_extension",
   "enable_hotwording=$enable_hotwording",
   "enable_plugins=$enable_plugins",
   "enable_print_preview=$enable_print_preview",
   "enable_printing=$_enable_printing",
   "enable_service_discovery=$enable_service_discovery",
   "enable_webrtc=$enable_webrtc",
   "enable_webvr=$enable_webvr",
   "mac_views_browser=$mac_views_browser",
   "safe_browsing_mode=$safe_browsing_mode",
   "use_vulcanize=$use_vulcanize",
 ]