Add missing header files to GN files

ui/gfx/ipc/skia/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.
 
 component("skia") {
   output_name = "gfx_ipc_skia"
 
   sources = [
+    "gfx_skia_ipc_export.h",
     "gfx_skia_param_traits.cc",
     "gfx_skia_param_traits.h",
   ]
 
   defines = [ "GFX_SKIA_IPC_IMPLEMENTATION" ]
 
   deps = [
     "//base",
     "//skia",
     "//ui/gfx",
     "//ui/gfx/geometry",
   ]
 
   public_deps = [
     "//ipc",
     "//ui/gfx/ipc",
   ]
 }