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

mojo/edk/system/simple_dispatcher.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/edk/system/simple_dispatcher.h"
 
 #include "base/logging.h"
 
 namespace mojo {
 namespace system {
@@ skipping 42 matching lines @@
 
 void SimpleDispatcher::RemoveAwakableImplNoLock(
     Awakable* awakable,
     HandleSignalsState* signals_state) {
   mutex().AssertHeld();
   awakable_list_.Remove(awakable);
   if (signals_state)
     *signals_state = GetHandleSignalsStateImplNoLock();
 }
 
+void SimpleDispatcher::RemoveAwakableWithContextImplNoLock(
+    Awakable* awakable,
+    uint64_t context,
+    HandleSignalsState* signals_state) {
+  mutex().AssertHeld();
+  awakable_list_.RemoveWithContext(awakable, context);
+  if (signals_state)
+    *signals_state = GetHandleSignalsStateImplNoLock();
+}
+
 }  // namespace system
 }  // namespace mojo