Work on Windows GN component build.

ppapi/thunk/BUILD.gn

 # Copyright 2015 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.
 
 source_set("thunk") {
+  # In GYP this is the same target as shared_impl. In GN these are split apart
+  # for clarity but to get component builds correct, targets must only depend
+  # on these via the shared_impl component.
+  # TODO(brettw) separate these when GYP compat is no longer required.
+  visibility = [ "//ppapi/shared_impl" ]
+
   sources = [
     "enter.cc",
     "enter.h",
     "ppb_audio_api.h",
     "ppb_audio_buffer_api.h",
     "ppb_audio_buffer_thunk.cc",
     "ppb_audio_config_api.h",
     "ppb_audio_config_thunk.cc",
     "ppb_audio_input_api.h",
     "ppb_audio_thunk.cc",
@@ skipping 166 matching lines @@
     sources += [
       "ppb_graphics_3d_thunk.cc",
       "ppb_host_resolver_private_thunk.cc",
       "ppb_tcp_server_socket_private_thunk.cc",
       "ppb_tcp_socket_private_thunk.cc",
       "ppb_udp_socket_private_thunk.cc",
       "ppb_x509_certificate_private_thunk.cc",
     ]
   }
 
-  defines = [ "PPAPI_THUNK_IMPLEMENTATION" ]
+  defines = [
+    # This target goes in the same library as shared_impl (in GYP they are the
+    # same).
+    "PPAPI_SHARED_IMPLEMENTATION",
+
+    "PPAPI_THUNK_IMPLEMENTATION",
+  ]
 }