Support external task cancellation mechanisms in base::Callback::IsCancelled

third_party/WebKit/Source/platform/WebTaskRunner.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 WebTaskRunner_h
 #define WebTaskRunner_h
 
 #include "base/callback_forward.h"
 #include "public/platform/WebCommon.h"
 #include "public/platform/WebTraceLocation.h"
@@ skipping 28 matching lines @@
   // This function is not thread safe. Call this on the thread that has posted
   // the task.
   void cancel();
 
   TaskHandle();
   ~TaskHandle();
 
   TaskHandle(TaskHandle&&);
   TaskHandle& operator=(TaskHandle&&);
 
+  class Runner;
+
  private:
-  class Runner;
   friend class WebTaskRunner;
 
   explicit TaskHandle(RefPtr<Runner>);
   RefPtr<Runner> m_runner;
 };
 
 // The blink representation of a chromium SingleThreadTaskRunner.
 class BLINK_PLATFORM_EXPORT WebTaskRunner {
  public:
   virtual ~WebTaskRunner() {}
@@ skipping 69 matching lines @@
                                  std::unique_ptr<WTF::Closure>)
       WARN_UNUSED_RETURN;
   TaskHandle postDelayedCancellableTask(const WebTraceLocation&,
                                         std::unique_ptr<WTF::Closure>,
                                         long long delayMs) WARN_UNUSED_RETURN;
 };
 
 }  // namespace blink
 
 #endif  // WebTaskRunner_h