Revert of Drop unecessary use of CrossThreadPersistent by CanvasAsyncBlobCreator.

third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.cpp

Index: third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.cpp
diff --git a/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.cpp b/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.cpp
index 007947c366e67c3bd4d36e2f8cf99ac28c9aa18f..01136649524082b8b79b83dda662a2a4852c957e 100644
--- a/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.cpp
+++ b/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.cpp
@@ -256,12 +256,20 @@
     ASSERT(isMainThread());
     Blob* resultBlob = Blob::create(m_encodedImage->data(), m_encodedImage->size(), convertMimeTypeEnumToString(m_mimeType));
     Platform::current()->mainThread()->getWebTaskRunner()->postTask(BLINK_FROM_HERE, bind(&BlobCallback::handleEvent, m_callback, resultBlob));
+    // Since toBlob is done, timeout events are no longer needed. So we clear
+    // non-GC members to allow teardown of CanvasAsyncBlobCreator.
+    m_data.clear();
+    m_callback.clear();
 }
 
 void CanvasAsyncBlobCreator::createNullAndInvokeCallback()
 {
     ASSERT(isMainThread());
     Platform::current()->mainThread()->getWebTaskRunner()->postTask(BLINK_FROM_HERE, bind(&BlobCallback::handleEvent, m_callback, nullptr));
+    // Since toBlob is done (failed), timeout events are no longer needed. So we
+    // clear non-GC members to allow teardown of CanvasAsyncBlobCreator.
+    m_data.clear();
+    m_callback.clear();
 }
 
 void CanvasAsyncBlobCreator::encodeImageOnEncoderThread(double quality)