Fix protocol for aborting and waiting for cancelable tasks.

src/cancelable-task.h

 // Copyright 2015 the V8 project 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 V8_CANCELABLE_TASK_H_
 #define V8_CANCELABLE_TASK_H_
 
 #include "include/v8-platform.h"
 #include "src/atomic-utils.h"
 #include "src/base/macros.h"
@@ skipping 25 matching lines @@
   //     removed.
   //
   // Returns {false} for (1) and (2), and {true} for (3).
   bool TryAbort(uint32_t id);
 
   // Cancels all remaining registered tasks and waits for tasks that are
   // already running.
   void CancelAndWait();
 
  private:
+  // Only called by {Cancelable} destructor. The task is done with executing,
+  // but needs to be removed.
+  void RemoveFinishedTask(uint32_t id);
+
   // To mitigate the ABA problem, the api refers to tasks through an id.
   uint32_t task_id_counter_;
 
   // A set of cancelable tasks that are currently registered.
   HashMap cancelable_tasks_;
 
   // Mutex and condition variable enabling concurrent register and removing, as
   // well as waiting for background tasks on {CancelAndWait}.
   base::ConditionVariable cancelable_tasks_barrier_;
   base::Mutex mutex_;
 
+  friend class Cancelable;
+
   DISALLOW_COPY_AND_ASSIGN(CancelableTaskManager);
 };
 
 
 class Cancelable {
  public:
   explicit Cancelable(CancelableTaskManager* parent);
   virtual ~Cancelable();
 
   // Never invoke after handing over the task to the platform! The reason is
@@ skipping 86 matching lines @@
  private:
   Isolate* isolate_;
   DISALLOW_COPY_AND_ASSIGN(CancelableIdleTask);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CANCELABLE_TASK_H_