Revert of Drop unecessary use of CrossThreadPersistent by CanvasAsyncBlobCreator.

third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.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.
 
 #include "core/CoreExport.h"
 #include "core/dom/DOMTypedArray.h"
 #include "core/fileapi/BlobCallback.h"
 #include "platform/geometry/IntSize.h"
 #include "platform/heap/Handle.h"
 #include "wtf/OwnPtr.h"
@@ skipping 24 matching lines @@
         IdleTaskSwitchedToMainThreadTask,
         IdleTaskNotSupported // Idle tasks are not implemented for some image types
     };
     // Methods are virtual for mocking in unit tests
     virtual void signalTaskSwitchInStartTimeoutEventForTesting() { }
     virtual void signalTaskSwitchInCompleteTimeoutEventForTesting() { }
 
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
         visitor->trace(m_data);
-        visitor->trace(m_callback);
     }
 
 protected:
     CanvasAsyncBlobCreator(DOMUint8ClampedArray* data, MimeType, const IntSize&, BlobCallback*);
     // Methods are virtual for unit testing
     virtual void scheduleInitiatePngEncoding();
     virtual void scheduleInitiateJpegEncoding(const double&);
     virtual void idleEncodeRowsPng(double deadlineSeconds);
     virtual void idleEncodeRowsJpeg(double deadlineSeconds);
     virtual void postDelayedTaskToMainThread(const WebTraceLocation&, std::unique_ptr<SameThreadClosure>, double delayMs);
@@ skipping 10 matching lines @@
 
     OwnPtr<PNGImageEncoderState> m_pngEncoderState;
     OwnPtr<JPEGImageEncoderState> m_jpegEncoderState;
     Member<DOMUint8ClampedArray> m_data;
     OwnPtr<Vector<unsigned char>> m_encodedImage;
     int m_numRowsCompleted;
 
     const IntSize m_size;
     size_t m_pixelRowStride;
     const MimeType m_mimeType;
-    Member<BlobCallback> m_callback;
+    CrossThreadPersistent<BlobCallback> m_callback;
 
     // PNG
     bool initializePngStruct();
     void encodeRowsPngOnMainThread(); // Similar to idleEncodeRowsPng without deadline
 
     // JPEG
     bool initializeJpegStruct(double quality);
     void encodeRowsJpegOnMainThread(); // Similar to idleEncodeRowsJpeg without deadline
 
     // WEBP
     void encodeImageOnEncoderThread(double quality);
 
     void idleTaskStartTimeoutEvent(double quality);
     void idleTaskCompleteTimeoutEvent();
 };
 
 } // namespace blink