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

mojo/edk/system/awakable_list.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/awakable_list.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "mojo/edk/system/awakable.h"
@@ skipping 52 matching lines @@
     if (it->awakable == awakable) {
       --last;
       std::swap(*it, *last);
     } else {
       ++it;
     }
   }
   awakables_.erase(last, awakables_.end());
 }
 
+void AwakableList::RemoveWithContext(Awakable* awakable, uint64_t context) {
+  // We allow a thread to wait on the same handle multiple times simultaneously,
+  // so we need to scan the entire list and remove all occurrences of |waiter|.
+  auto last = awakables_.end();
+  for (AwakeInfoList::iterator it = awakables_.begin(); it != last;) {
+    if (it->awakable == awakable && it->context == context) {
+      --last;
+      std::swap(*it, *last);
+    } else {
+      ++it;
+    }
+  }
+  awakables_.erase(last, awakables_.end());
+}
+
 }  // namespace system
 }  // namespace mojo