Reland 95309. Add a template to handle properly issuing completion callbacks.

ppapi/proxy/ppb_file_system_proxy.cc

 // Copyright (c) 2011 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.
 
 #include "ppapi/proxy/ppb_file_system_proxy.h"
 
 #include "base/message_loop.h"
 #include "base/task.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/c/ppb_file_system.h"
@@ skipping 156 matching lines @@
     return;
   PP_Resource resource = enter.functions()->CreateFileSystem(
       instance, static_cast<PP_FileSystemType>(type));
   if (!resource)
     return;  // CreateInfo default constructor initializes to 0.
   result->SetHostResource(instance, resource);
 }
 
 void PPB_FileSystem_Proxy::OnMsgOpen(const HostResource& host_resource,
                                      int64_t expected_size) {
-  EnterHostFromHostResource<PPB_FileSystem_API> enter(host_resource);
-  if (enter.failed())
-    return;
-
-  CompletionCallback callback = callback_factory_.NewOptionalCallback(
+  EnterHostFromHostResourceForceCallback<PPB_FileSystem_API> enter(
+      host_resource, callback_factory_,
       &PPB_FileSystem_Proxy::OpenCompleteInHost, host_resource);
-  int32_t result = enter.object()->Open(expected_size,
-                                        callback.pp_completion_callback());
-  if (result != PP_OK_COMPLETIONPENDING)
-    callback.Run(result);
+  if (enter.succeeded())
+    enter.SetResult(enter.object()->Open(expected_size, enter.callback()));
 }
 
 // Called in the plugin to handle the open callback.
 void PPB_FileSystem_Proxy::OnMsgOpenComplete(const HostResource& host_resource,
                                              int32_t result) {
   EnterPluginFromHostResource<PPB_FileSystem_API> enter(host_resource);
   if (enter.succeeded())
     static_cast<FileSystem*>(enter.object())->OpenComplete(result);
 }
 
 void PPB_FileSystem_Proxy::OpenCompleteInHost(
     int32_t result,
     const HostResource& host_resource) {
   dispatcher()->Send(new PpapiMsg_PPBFileSystem_OpenComplete(
       INTERFACE_ID_PPB_FILE_SYSTEM, host_resource, result));
 }
 
 }  // namespace proxy
 }  // namespace pp