Modify bindings to enforce that an error handler callback is only set after binding to a msg pipe.

mojo/public/cpp/bindings/associated_binding.h

 // Copyright 2015 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_ASSOCIATED_BINDING_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_ASSOCIATED_BINDING_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "mojo/public/cpp/bindings/associated_group.h"
@@ skipping 72 matching lines @@
         [this]() { connection_error_handler_.Run(); });
 
     stub_.serialization_context()->router = endpoint_client_->router();
   }
 
   // Closes the associated interface. Puts this object into a state where it can
   // be rebound.
   void Close() {
     DCHECK(endpoint_client_);
     endpoint_client_.reset();
+    connection_error_handler_.reset();
   }
 
   // Unbinds and returns the associated interface request so it can be
   // used in another context, such as on another thread or with a different
   // implementation. Puts this object into a state where it can be rebound.
   AssociatedInterfaceRequest<Interface> Unbind() {
     DCHECK(endpoint_client_);
 
     AssociatedInterfaceRequest<Interface> request;
     internal::AssociatedInterfaceRequestHelper::SetHandle(
         &request, endpoint_client_->PassHandle());
 
     endpoint_client_.reset();
+    connection_error_handler_.reset();
 
     return request.Pass();
   }
 
   // Sets an error handler that will be called if a connection error occurs.
+  //
+  // This method may only be called after this AssociatedBinding has been bound
+  // to a message pipe. The error handler will be reset when this
+  // AssociatedBinding is unbound or closed.
   void set_connection_error_handler(const Closure& error_handler) {
+    DCHECK(is_bound());
     connection_error_handler_ = error_handler;
   }
 
   // Returns the interface implementation that was previously specified.
   Interface* impl() { return impl_; }
 
   // Indicates whether the associated binding has been completed.
   bool is_bound() const { return !!endpoint_client_; }
 
   // Returns the associated group that this object belongs to. Returns null if
   // the object is not bound.
   AssociatedGroup* associated_group() {
     return endpoint_client_ ? endpoint_client_->associated_group() : nullptr;
   }
 
  private:
   scoped_ptr<internal::InterfaceEndpointClient> endpoint_client_;
 
   typename Interface::Stub_ stub_;
   Interface* impl_;
   Closure connection_error_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(AssociatedBinding);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_ASSOCIATED_BINDING_H_