Simplify //mojo/public/c/system targets

mojo/public/platform/native/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_sdk.gni")
 
-mojo_sdk_source_set("system_thunks") {
-  mojo_sdk_visibility = [
-    "mojo/public/c/system:for_component",
-    "mojo/public/c/system:for_shared_library",
-  ]
-
+mojo_sdk_source_set("system") {
   sources = [
     "system_thunks.h",
     "system_thunks.cc",
   ]
   defines = [ "MOJO_SYSTEM_IMPLEMENTATION" ]
   mojo_sdk_deps = [ "mojo/public/c/system" ]
 
   # The GYP target analogous to this one builds this code into a
   # static library.  When building for Android, both the GYP and GN
   # builds add --exclude-libs=ALL globally, which means that all
   # symbols in static libraries are excluded from export.  That's a
   # problem, as code outside this target needs to be able to call
   # MojoSetSystemThunks(). Therefore, the GYP target needs to specifiy
   # that all dependent targets remove that link flag. Since GN uses a
   # source_set here, this flag change is not needed.
 }
 
-mojo_sdk_source_set("gles2_thunks") {
-  mojo_sdk_visibility = [ "mojo/public/gles2:for_shared_library" ]
-
+mojo_sdk_source_set("gles2") {
   sources = [
     "gles2_thunks.cc",
     "gles2_thunks.h",
     "gles2_impl_thunks.cc",
     "gles2_impl_thunks.h",
     "gles2_impl_chromium_texture_mailbox_thunks.cc",
     "gles2_impl_chromium_texture_mailbox_thunks.h",
     "gles2_impl_chromium_sync_point_thunks.cc",
     "gles2_impl_chromium_sync_point_thunks.h",
   ]
 
   defines = [ "MOJO_GLES2_IMPLEMENTATION" ]
 
   configs = [ "//third_party/khronos:khronos_headers" ]
 
   mojo_sdk_deps = [
     "mojo/public/c/gles2:headers",
     "mojo/public/c/environment",
     "mojo/public/c/system",
   ]
 
   if (is_mac) {
     # TODO(GYP): Make it a run-path dependent library.
     # 'DYLIB_INSTALL_NAME_BASE': '@loader_path',
   }
 }