CPP bindings: DCHECK when a Callback is destructed without being invoked

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

 // 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.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_CONNECTOR_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_CONNECTOR_H_
 
 #include "mojo/public/c/environment/async_waiter.h"
 #include "mojo/public/cpp/bindings/lib/message_queue.h"
 #include "mojo/public/cpp/bindings/message.h"
@@ skipping 45 matching lines @@
   bool encountered_error() const { return error_; }
 
   // Closes the pipe, triggering the error state. Connector is put into a
   // quiescent state.
   void CloseMessagePipe();
 
   // Releases the pipe, not triggering the error state. Connector is put into
   // a quiescent state.
   ScopedMessagePipeHandle PassMessagePipe();
 
+  // Is the connector bound to a MessagePipe handle?
+  bool is_valid() const { return message_pipe_.is_valid(); }
+
   // Waits for the next message on the pipe, blocking until one arrives or an
   // error happens. Returns |true| if a message has been delivered, |false|
   // otherwise.
   bool WaitForIncomingMessage();
 
   // MessageReceiver implementation:
   bool Accept(Message* message) override;
 
  private:
   static void CallOnHandleReady(void* closure, MojoResult result);
@@ skipping 28 matching lines @@
   // of dispatching an incoming message.
   bool* destroyed_flag_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(Connector);
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_CONNECTOR_H_