[mojo-edk] Prevent watching an invalid FD on early broker pipe closure

mojo/edk/system/node_controller.cc

Index: mojo/edk/system/node_controller.cc
diff --git a/mojo/edk/system/node_controller.cc b/mojo/edk/system/node_controller.cc
index 2368dab2a5ceb22a36d21ea134de3e291fb68aa2..a1fe420ed50a333aa66409375f06b62a6079dea8 100644
--- a/mojo/edk/system/node_controller.cc
+++ b/mojo/edk/system/node_controller.cc
@@ -202,6 +202,14 @@ void NodeController::ConnectToParent(ScopedPlatformHandle platform_handle) {
   platform_handle = broker_->GetParentPlatformHandle();
   UMA_HISTOGRAM_TIMES("Mojo.System.GetParentPlatformHandleSyncTime",
                       timer.Elapsed());
+
+  if (!platform_handle.is_valid()) {
+    // Most likely the browser side of the channel has already been closed and
+    // the broker was unable to negotiate a NodeChannel pipe. In this case we
+    // can cancel parent connection.
+    DVLOG(1) << "Cannot connect to invalid parent channel.";
+    return;
+  }
 #endif
 
   io_task_runner_->PostTask(