Give AwakableList's wake-up method the old state in addition to the new state.

mojo/edk/system/simple_dispatcher.h

Index: mojo/edk/system/simple_dispatcher.h
diff --git a/mojo/edk/system/simple_dispatcher.h b/mojo/edk/system/simple_dispatcher.h
index 4501e8ca98b61aa053346b95dfaa07e584a3cf02..95942cfa0f6c1e8903f711b85a705232f67a4104 100644
--- a/mojo/edk/system/simple_dispatcher.h
+++ b/mojo/edk/system/simple_dispatcher.h
@@ -9,6 +9,7 @@
 
 #include "mojo/edk/system/awakable_list.h"
 #include "mojo/edk/system/dispatcher.h"
+#include "mojo/edk/system/handle_signals_state.h"
 #include "mojo/edk/util/thread_annotations.h"
 #include "mojo/public/cpp/system/macros.h"
 
@@ -24,9 +25,10 @@ class SimpleDispatcher : public Dispatcher {
   SimpleDispatcher();
   ~SimpleDispatcher() override;
 
-  // To be called by subclasses when the state changes (so
-  // |GetHandleSignalsStateImplNoLock()| should be checked again).
-  void HandleSignalsStateChangedNoLock() MOJO_EXCLUSIVE_LOCKS_REQUIRED(mutex());
+  // To be called by subclasses when the state changes.
+  void OnHandleSignalsStateChangeNoLock(const HandleSignalsState& old_state,
+                                        const HandleSignalsState& new_state)
+      MOJO_EXCLUSIVE_LOCKS_REQUIRED(mutex());
 
   // |Dispatcher| protected methods:
   void CancelAllStateNoLock() override;