Make it possible to remove an Awakable with a specific "context" from a Dispatcher.

mojo/edk/system/data_pipe.h

Index: mojo/edk/system/data_pipe.h
diff --git a/mojo/edk/system/data_pipe.h b/mojo/edk/system/data_pipe.h
index 63083b7b0bddcc72bcd9d4f8409ee905f73fa01c..3853efb50ea79eb5ce7599549f4bf31b270dc6e5 100644
--- a/mojo/edk/system/data_pipe.h
+++ b/mojo/edk/system/data_pipe.h
@@ -121,6 +121,9 @@ class DataPipe final : public ChannelEndpointClient {
                                  HandleSignalsState* signals_state);
   void ProducerRemoveAwakable(Awakable* awakable,
                               HandleSignalsState* signals_state);
+  void ProducerRemoveAwakableWithContext(Awakable* awakable,
+                                         uint64_t context,
+                                         HandleSignalsState* signals_state);
   void ProducerStartSerialize(Channel* channel,
                               size_t* max_size,
                               size_t* max_platform_handles);
@@ -156,6 +159,9 @@ class DataPipe final : public ChannelEndpointClient {
                                  HandleSignalsState* signals_state);
   void ConsumerRemoveAwakable(Awakable* awakable,
                               HandleSignalsState* signals_state);
+  void ConsumerRemoveAwakableWithContext(Awakable* awakable,
+                                         uint64_t context,
+                                         HandleSignalsState* signals_state);
   void ConsumerStartSerialize(Channel* channel,
                               size_t* max_size,
                               size_t* max_platform_handles);