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diff --git a/dom/media/imagecapture/CaptureTask.h b/dom/media/imagecapture/CaptureTask.h
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+++ b/dom/media/imagecapture/CaptureTask.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef CAPTURETASK_H
+#define CAPTURETASK_H
+
+#include "MediaStreamGraph.h"
+#include "MediaStreamListener.h"
+#include "PrincipalChangeObserver.h"
+#include "MediaStreamVideoSink.h"
+
+namespace mozilla {
+
+namespace dom {
+class Blob;
+class ImageCapture;
+class MediaStreamTrack;
+} // namespace dom
+
+/**
+ * CaptureTask retrieves image from MediaStream and encodes the image to jpeg in
+ * ImageEncoder. The whole procedures start at AttachTrack(), it will add this
+ * class into MediaStream and retrieves an image in MediaStreamGraph thread.
+ * Once the image is retrieved, it will be sent to ImageEncoder and the encoded
+ * blob will be sent out via encoder callback in main thread.
+ *
+ * CaptureTask holds a reference of ImageCapture to ensure ImageCapture won't be
+ * released during the period of the capturing process described above.
+ */
+class CaptureTask : public MediaStreamVideoSink,
+                    public dom::PrincipalChangeObserver<dom::MediaStreamTrack>
+{
+public:
+  class MediaStreamEventListener;
+
+  // MediaStreamVideoSink methods.
+  void SetCurrentFrames(const VideoSegment& aSegment) override;
+  void ClearFrames() override {}
+
+  // PrincipalChangeObserver<MediaStreamTrack> method.
+  void PrincipalChanged(dom::MediaStreamTrack* aMediaStreamTrack) override;
+
+  // CaptureTask methods.
+
+  // It is called when aBlob is ready to post back to script in company with
+  // aRv == NS_OK. If aRv is not NS_OK, it will post an error event to script.
+  //
+  // Note:
+  //   this function should be called on main thread.
+  nsresult TaskComplete(already_AddRefed<dom::Blob> aBlob, nsresult aRv);
+
+  // Add listeners into MediaStreamTrack and PrincipalChangeObserver.
+  // It should be on main thread only.
+  void AttachTrack();
+
+  // Remove listeners from MediaStreamTrack and PrincipalChangeObserver.
+  // It should be on main thread only.
+  void DetachTrack();
+
+  // CaptureTask should be created on main thread.
+  explicit CaptureTask(dom::ImageCapture* aImageCapture);
+
+protected:
+  virtual ~CaptureTask() {}
+
+  // Post a runnable on main thread to end this task and call TaskComplete to post
+  // error event to script. It is called off-main-thread.
+  void PostTrackEndEvent();
+
+  // The ImageCapture associates with this task. This reference count should not
+  // change in this class unless it clears this reference after a blob or error
+  // event to script.
+  RefPtr<dom::ImageCapture> mImageCapture;
+
+  RefPtr<MediaStreamEventListener> mEventListener;
+
+  // True when an image is retrieved from MediaStreamGraph or MediaStreamGraph
+  // sends a track finish, end, or removed event.
+  bool mImageGrabbedOrTrackEnd;
+
+  // True after MediaStreamTrack principal changes while waiting for a photo
+  // to finish and we should raise a security error.
+  bool mPrincipalChanged;
+};
+
+} // namespace mozilla
+
+#endif // CAPTURETASK_H