Add missing header files to GN files

ui/gfx/ipc/color/BUILD.gn

 # Copyright 2016 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("color") {
   output_name = "gfx_ipc_color"
 
   sources = [
+    "gfx_ipc_color_export.h",
     "gfx_param_traits.cc",
     "gfx_param_traits.h",
     "gfx_param_traits_macros.h",
   ]
 
   defines = [ "GFX_IPC_COLOR_IMPLEMENTATION" ]
 
   public_deps = [
     "//base",
     "//ipc",
     "//ui/gfx:gfx",
   ]
 }