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

mojo/public/cpp/bindings/binding.h

Index: mojo/public/cpp/bindings/binding.h
diff --git a/mojo/public/cpp/bindings/binding.h b/mojo/public/cpp/bindings/binding.h
index a982bdbd4b10642837f8e1306253f0832f43e95b..18637c1d13abbd25a2a36c9c9e0a8bac53ce805c 100644
--- a/mojo/public/cpp/bindings/binding.h
+++ b/mojo/public/cpp/bindings/binding.h
@@ -156,6 +156,7 @@ class Binding : public ErrorHandler {
   // Closes the message pipe that was previously bound. Put this object into a
   // state where it can be rebound to a new pipe.
   void Close() {
+    stub_.Close();
     MOJO_DCHECK(internal_router_);
     internal_router_->CloseMessagePipe();
     DestroyRouter();
@@ -182,6 +183,13 @@ class Binding : public ErrorHandler {
 
   // Implements the |Binding|'s response to a connection error.
   void OnConnectionError() override {
+    // Note that it is important that we tell |stub_| that there was a
+    // connection error before we tell |error_handler_|. This is because
+    // in response |error_handler_| may destroy a Callback that hasn't been
+    // run and this will cause |stub_| to DCHECK unless it also knows that
+    // this happened for a legitimate reason, namely that a connection error
+    // occurred.
+    stub_.OnConnectionError();
     if (error_handler_)
       error_handler_->OnConnectionError();
   }