GN: Replace mojo/system.gni with forwarding groups

mojo/examples/pepper_container_app/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("//mojo/system.gni")
-
 # GYP version: mojo/mojo_examples.gypi:mojo_pepper_container_app
 shared_library("pepper_container_app") {
   output_name = "mojo_pepper_container_app"
 
   sources = [
     # Source files from ppapi/.
     # An alternative is to depend on
     # "//ppapi/ppapi_shared', but that target includes
     # a lot of things that we don't need.
     # TODO(yzshen): Consider extracting these files into a separate target
@@ skipping 71 matching lines @@
 
   deps = [
     "//base",
     "//base/third_party/dynamic_annotations",
     "//gpu/command_buffer/common",
     "//ppapi:ppapi_c",
     # TODO(GYP):
     # "//ppapi:ppapi_example_gles2_spinning_cube",
     "//mojo/application",
     "//mojo/common",
+    "//mojo/public/c/system:for_shared_library",
+    "//mojo/public/gles2:for_shared_library",
     "//mojo/services/public/interfaces/geometry",
     "//mojo/services/public/interfaces/gpu",
     "//mojo/services/public/interfaces/native_viewport",
     "//ui/events:events_base",
-  ] + mojo_system_for_shared_library + mojo_gles2_for_shared_library
+  ]
 }