Support generic synchronization against an IPC::Channel

ipc/ipc_message_pipe_reader.h

Index: ipc/ipc_message_pipe_reader.h
diff --git a/ipc/ipc_message_pipe_reader.h b/ipc/ipc_message_pipe_reader.h
index cd88149801465a10a1be4981905d3a91d10e2009..8425fed172927f5a265a54bee409811d0c05a5fe 100644
--- a/ipc/ipc_message_pipe_reader.h
+++ b/ipc/ipc_message_pipe_reader.h
@@ -86,6 +86,9 @@ class IPC_EXPORT MessagePipeReader : public NON_EXPORTED_BASE(mojom::Channel) {
   void GetRemoteInterface(const std::string& name,
                           mojo::ScopedInterfaceEndpointHandle handle);
 
+  // Sends an Event to be signalled ASAP from the other side of the channel.
+  void SendEventToSignal(mojo::common::mojom::EventPtr event);
+
   base::ProcessId GetPeerPid() const { return peer_pid_; }
 
   mojom::Channel* sender() const { return sender_.get(); }
@@ -103,6 +106,7 @@ class IPC_EXPORT MessagePipeReader : public NON_EXPORTED_BASE(mojom::Channel) {
   void GetAssociatedInterface(
       const std::string& name,
       mojom::GenericInterfaceAssociatedRequest request) override;
+  void SignalEvent(mojo::common::mojom::EventPtr event) override;
 
   // |delegate_| is null once the message pipe is closed.
   Delegate* delegate_;