Use OnceCallback for Mojo binding connection error handlers.

mojo/public/cpp/bindings/strong_binding.h

 // Copyright 2014 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.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_STRONG_BINDING_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_STRONG_BINDING_H_
 
 #include <memory>
 #include <string>
 #include <utility>
@@ skipping 41 matching lines @@
       InterfaceRequest<Interface> request) {
     StrongBinding* binding =
         new StrongBinding(std::move(impl), std::move(request));
     return binding->weak_factory_.GetWeakPtr();
   }
 
   // Note: The error handler must not delete the interface implementation.
   //
   // This method may only be called after this StrongBinding has been bound to a
   // message pipe.
-  void set_connection_error_handler(const base::Closure& error_handler) {
+  void set_connection_error_handler(base::OnceClosure error_handler) {
     DCHECK(binding_.is_bound());
-    connection_error_handler_ = error_handler;
+    connection_error_handler_ = std::move(error_handler);
     connection_error_with_reason_handler_.Reset();
   }
 
   void set_connection_error_with_reason_handler(
-      const ConnectionErrorWithReasonCallback& error_handler) {
+      ConnectionErrorWithReasonCallback error_handler) {
     DCHECK(binding_.is_bound());
-    connection_error_with_reason_handler_ = error_handler;
+    connection_error_with_reason_handler_ = std::move(error_handler);
     connection_error_handler_.Reset();
   }
 
   // Forces the binding to close. This destroys the StrongBinding instance.
   void Close() { delete this; }
 
   Interface* impl() { return impl_.get(); }
 
   // Sends a message on the underlying message pipe and runs the current
   // message loop until its response is received. This can be used in tests to
   // verify that no message was sent on a message pipe in response to some
   // stimulus.
   void FlushForTesting() { binding_.FlushForTesting(); }
 
  private:
   StrongBinding(std::unique_ptr<Interface> impl,
                 InterfaceRequest<Interface> request)
       : impl_(std::move(impl)),
         binding_(impl_.get(), std::move(request)),
         weak_factory_(this) {
     binding_.set_connection_error_with_reason_handler(
         base::Bind(&StrongBinding::OnConnectionError, base::Unretained(this)));
   }
 
   ~StrongBinding() {}
 
   void OnConnectionError(uint32_t custom_reason,
                          const std::string& description) {
-    if (!connection_error_handler_.is_null())
-      connection_error_handler_.Run();
-    else if (!connection_error_with_reason_handler_.is_null())
-      connection_error_with_reason_handler_.Run(custom_reason, description);
+    if (connection_error_handler_) {
+      std::move(connection_error_handler_).Run();
+    } else if (connection_error_with_reason_handler_) {
+      std::move(connection_error_with_reason_handler_)
+          .Run(custom_reason, description);
+    }
     Close();
   }
 
   std::unique_ptr<Interface> impl_;
-  base::Closure connection_error_handler_;
+  base::OnceClosure connection_error_handler_;
   ConnectionErrorWithReasonCallback connection_error_with_reason_handler_;
   Binding<Interface> binding_;
   base::WeakPtrFactory<StrongBinding> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(StrongBinding);
 };
 
 template <typename Interface, typename Impl>
 StrongBindingPtr<Interface> MakeStrongBinding(
     std::unique_ptr<Impl> impl,
     InterfaceRequest<Interface> request) {
   return StrongBinding<Interface>::Create(std::move(impl), std::move(request));
 }
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_STRONG_BINDING_H_