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

ppapi/proxy/ppb_url_loader_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_url_loader_proxy.h"
 
 #include <algorithm>
 #include <deque>
 #include <vector>
 
@@ skipping 499 matching lines @@
   // This heap object will get deleted by the callback handler.
   // TODO(brettw) this will be leaked if the plugin closes the resource!
   // (Also including the plugin unloading and having the resource implicitly
   // destroyed. Depending on the cleanup ordering, we may not need the weak
   // pointer here.)
   ReadCallbackInfo* info = new ReadCallbackInfo;
   info->resource = loader;
   // TODO(brettw) have a way to check for out-of-memory.
   info->read_buffer.resize(bytes_to_read);
 
-  CompletionCallback callback = callback_factory_.NewOptionalCallback(
-      &PPB_URLLoader_Proxy::OnReadCallback, info);
-
-  EnterHostFromHostResource<PPB_URLLoader_API> enter(loader);
-  int32_t result = PP_ERROR_BADRESOURCE;
+  EnterHostFromHostResourceForceCallback<PPB_URLLoader_API> enter(
+      loader, callback_factory_, &PPB_URLLoader_Proxy::OnReadCallback, info);
   if (enter.succeeded()) {
-    result = enter.object()->ReadResponseBody(
+    enter.SetResult(enter.object()->ReadResponseBody(
         const_cast<char*>(info->read_buffer.c_str()),
-        bytes_to_read, callback.pp_completion_callback());
-  }
-  if (result != PP_OK_COMPLETIONPENDING) {
-    // Send error (or perhaps success for synchronous reads) back to plugin.
-    // The callback function is already set up to do this and also delete the
-    // callback info.
-    callback.Run(result);
+        bytes_to_read, enter.callback()));
   }
 }
 
 void PPB_URLLoader_Proxy::OnMsgFinishStreamingToFile(
     const HostResource& loader,
     uint32_t serialized_callback) {
   EnterHostFromHostResource<PPB_URLLoader_API> enter(loader);
   PP_CompletionCallback callback = ReceiveCallback(serialized_callback);
   int32_t result = PP_ERROR_BADRESOURCE;
   if (enter.succeeded())
@@ skipping 41 matching lines @@
   info->read_buffer.resize(bytes_read);
 
   dispatcher()->Send(new PpapiMsg_PPBURLLoader_ReadResponseBody_Ack(
       INTERFACE_ID_PPB_URL_LOADER, info->resource, result, info->read_buffer));
 
   delete info;
 }
 
 }  // namespace proxy
 }  // namespace pp