Require commas between items in a GN list.

ui/gfx/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/ui.gni")
 if (is_android) {
   import("//build/config/android/config.gni")
 }
 
 # Several targets want to include this header file, and some of them are
@@ skipping 253 matching lines @@
       "codec/jpeg_codec.h",
     ]
   } else {
     deps += [ "//third_party/libjpeg" ]
   }
 
   # Android.
   if (is_android) {
     sources -= [
       "animation/throb_animation.cc",
-      "canvas_skia.cc"
+      "canvas_skia.cc",
       "display_observer.cc",
       "selection_model.cc",
     ]
 
     if (use_aura) {
       sources -= [ "screen_android.cc" ]
     } else {
       sources -= [ "path.cc" ]
     }
 
@@ skipping 166 matching lines @@
       "x/x11_atom_cache.h",
       "x/x11_error_tracker.cc",
       "x/x11_error_tracker.h",
       "x/x11_types.cc",
       "x/x11_types.h",
     ]
 
     configs += [ "//build/config/linux:x11" ]
   }
 }