ChannelMojo: Handle errors in pending message processing.

ipc/mojo/ipc_channel_mojo.h

Index: ipc/mojo/ipc_channel_mojo.h
diff --git a/ipc/mojo/ipc_channel_mojo.h b/ipc/mojo/ipc_channel_mojo.h
index 22c56a9e6894643e51f6f3838131dc6da513c8ce..95e9ed07007b177ab52905779eb616a38470aba1 100644
--- a/ipc/mojo/ipc_channel_mojo.h
+++ b/ipc/mojo/ipc_channel_mojo.h
@@ -105,6 +105,10 @@ class IPC_MOJO_EXPORT ChannelMojo : public Channel {
               Listener* listener,
               scoped_refptr<base::TaskRunner> io_thread_task_runner);
 
+  // Be virtual for testing.
+  virtual scoped_ptr<internal::MessageReader> CreateMessageReader(
+      mojo::ScopedMessagePipeHandle pipe);
+
  private:
   struct ChannelInfoDeleter {
     void operator()(mojo::embedder::ChannelInfo* ptr) const;