C++ bindings: support using a callback as connection error handler.

mojo/public/cpp/bindings/lib/connector.cc

 // Copyright 2013 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 "mojo/public/cpp/bindings/lib/connector.h"
 
 #include "mojo/public/cpp/bindings/error_handler.h"
 #include "mojo/public/cpp/environment/logging.h"
 
 namespace mojo {
 namespace internal {
 
 // ----------------------------------------------------------------------------
 
 Connector::Connector(ScopedMessagePipeHandle message_pipe,
                      const MojoAsyncWaiter* waiter)
-    : error_handler_(nullptr),
-      waiter_(waiter),
+    : waiter_(waiter),
       message_pipe_(message_pipe.Pass()),
       incoming_receiver_(nullptr),
       async_wait_id_(0),
       error_(false),
       drop_writes_(false),
       enforce_errors_from_incoming_receiver_(true),
       destroyed_flag_(nullptr) {
   // Even though we don't have an incoming receiver, we still want to monitor
   // the message pipe to know if is closed or encounters an error.
   WaitToReadMore();
@@ skipping 162 matching lines @@
   if (!async_wait_id_)
     return;
 
   waiter_->CancelWait(async_wait_id_);
   async_wait_id_ = 0;
 }
 
 void Connector::NotifyError() {
   error_ = true;
   CloseMessagePipe();
-  if (error_handler_)
-    error_handler_->OnConnectionError();
+  connection_error_handler_.Run();
 }
 
 }  // namespace internal
 }  // namespace mojo