Graceful idle callback cancellation with invalid IDs.

third_party/WebKit/Source/core/dom/ScriptedIdleTaskController.h

 // Copyright 2015 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.
 
 #ifndef ScriptedIdleTaskController_h
 #define ScriptedIdleTaskController_h
 
 #include "core/dom/ActiveDOMObject.h"
 #include "core/dom/IdleDeadline.h"
 #include "platform/Timer.h"
@@ skipping 25 matching lines @@
     // ActiveDOMObject interface.
     void stop() override;
     void suspend() override;
     void resume() override;
 
     void callbackFired(CallbackId, double deadlineSeconds, IdleDeadline::CallbackType);
 
 private:
     explicit ScriptedIdleTaskController(ExecutionContext*);
 
+    int nextCallbackId();
+
+    bool isValidCallbackId(int id)
+    {
+        using Traits = HashTraits<CallbackId>;
+        return !Traits::isDeletedValue(id) && !WTF::isHashTraitsEmptyValue<Traits, CallbackId>(id);
+    }
+
     void runCallback(CallbackId, double deadlineSeconds, IdleDeadline::CallbackType);
 
     WebScheduler* m_scheduler; // Not owned.
     HeapHashMap<CallbackId, Member<IdleRequestCallback>> m_callbacks;
     Vector<CallbackId> m_pendingTimeouts;
     CallbackId m_nextCallbackId;
     bool m_suspended;
 };
 
 } // namespace blink
 
 #endif // ScriptedIdleTaskController_h