Support generic synchronization against an IPC::Channel

ipc/ipc_channel_proxy.h

Index: ipc/ipc_channel_proxy.h
diff --git a/ipc/ipc_channel_proxy.h b/ipc/ipc_channel_proxy.h
index c90a4c639ba8352836658d93c64c275c177b915d..8b1d3089c7c8871987d6d657a69e4f744ae785b8 100644
--- a/ipc/ipc_channel_proxy.h
+++ b/ipc/ipc_channel_proxy.h
@@ -22,6 +22,7 @@
 #include "ipc/ipc_endpoint.h"
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_sender.h"
+#include "mojo/common/event.mojom.h"
 #include "mojo/public/cpp/bindings/associated_group.h"
 #include "mojo/public/cpp/bindings/associated_interface_request.h"
 #include "mojo/public/cpp/bindings/scoped_interface_endpoint_handle.h"
@@ -160,6 +161,11 @@ class IPC_EXPORT ChannelProxy : public Endpoint, public base::NonThreadSafe {
   void AddFilter(MessageFilter* filter);
   void RemoveFilter(MessageFilter* filter);
 
+  // Sends a message to the remote endpoint and returns an Event pipe which will
+  // Signal() once as soon as the remote endpoint receives the message. This
+  // can be used to synchronize against the Channel's message FIFO.
+  mojo::common::mojom::EventRequest CreateSynchronizationEvent();
+
   using GenericAssociatedInterfaceFactory =
       base::Callback<void(mojo::ScopedInterfaceEndpointHandle)>;
 
@@ -274,6 +280,9 @@ class IPC_EXPORT ChannelProxy : public Endpoint, public base::NonThreadSafe {
         const std::string& name,
         mojo::ScopedInterfaceEndpointHandle handle);
 
+    // Sends an Event to be signaled by the remote end.
+    void SendEventToSignal(mojo::common::mojom::EventPtr event);
+
    protected:
     friend class base::RefCountedThreadSafe<Context>;
     ~Context() override;