Make sure channel-associated interface pointers are always safe to call.

ipc/ipc_channel_mojo.cc

Index: ipc/ipc_channel_mojo.cc
diff --git a/ipc/ipc_channel_mojo.cc b/ipc/ipc_channel_mojo.cc
index d0129e3fe0833596ac3b576886f6d3e4ca54fd8f..ab376f4bdc46a697d939694e7fcfe81993bcbfa5 100644
--- a/ipc/ipc_channel_mojo.cc
+++ b/ipc/ipc_channel_mojo.cc
@@ -479,8 +479,14 @@ void ChannelMojo::AddGenericAssociatedInterface(
 void ChannelMojo::GetGenericRemoteAssociatedInterface(
     const std::string& name,
     mojo::ScopedInterfaceEndpointHandle handle) {
-  if (message_reader_)
+  if (message_reader_) {
     message_reader_->GetRemoteInterface(name, std::move(handle));
+  } else {
+    // Attach the associated interface to a disconnected pipe, so that the
+    // associated interface pointer can be used to make calls (which are
+    // dropped).
+    mojo::GetIsolatedInterface(std::move(handle));
+  }
 }
 
 }  // namespace IPC