Add missing dependency for gpu.

mojo/gpu/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.
 
 static_library("gpu") {
   sources = [
     "gl_context.cc",
     "gl_context.h",
     "gl_texture.cc",
     "gl_texture.h",
   ]
 
   deps = [
     "//base",
     "//gpu/command_buffer/client:gles2_interface",
     "//gpu/command_buffer/common",
     "//mojo/environment:chromium",
     "//mojo/public/c/system:for_shared_library",
+    "//mojo/public/cpp/application",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/environment",
     "//mojo/public/cpp/system",
     "//mojo/public/cpp/utility",
     "//mojo/public/gles2:for_shared_library",
     "//mojo/services/public/interfaces/gpu",
   ]
 }