NaCl cleanup: Split out irt_interfaces.cc from irt_ppapi.cc

ppapi/proxy/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.
 
 config("proxy_implementation") {
   defines = [ "PPAPI_PROXY_IMPLEMENTATION" ]
 }
 
 component("proxy") {
   output_name = "ppapi_proxy"
@@ skipping 178 matching lines @@
     "video_frame_resource.cc",
     "video_frame_resource.h",
     "video_source_resource.cc",
     "video_source_resource.h",
     "websocket_resource.cc",
     "websocket_resource.h",
   ]
 
   if (is_nacl) {
     sources += [
+      "../nacl_irt/irt_interfaces.cc",
+      "../nacl_irt/irt_interfaces.h",
       "../nacl_irt/irt_ppapi.cc",
       "../nacl_irt/irt_ppapi.h",
       "../nacl_irt/irt_start.cc",
       "../nacl_irt/manifest_service.cc",
       "../nacl_irt/manifest_service.h",
       "../nacl_irt/plugin_main.cc",
       "../nacl_irt/plugin_main.h",
       "../nacl_irt/plugin_startup.cc",
       "../nacl_irt/plugin_startup.h",
       "../nacl_irt/ppapi_dispatcher.cc",
@@ skipping 147 matching lines @@
   deps = [
     "//base/test:test_support",
     "//ipc",
     "//ipc:test_support",
     "//ppapi/proxy",
     "//ppapi/shared_impl",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }