Define frame subscription interface and implementation on Mac

content/port/browser/render_widget_host_view_frame_subscriber.h

Index: content/port/browser/render_widget_host_view_frame_subscriber.h
diff --git a/content/port/browser/render_widget_host_view_frame_subscriber.h b/content/port/browser/render_widget_host_view_frame_subscriber.h
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+// Copyright (c) 2012 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 CONTENT_PORT_BROWSER_RENDER_WIDGET_HOST_VIEW_FRAME_SUBSCRIBER_H_
+#define CONTENT_PORT_BROWSER_RENDER_WIDGET_HOST_VIEW_FRAME_SUBSCRIBER_H_
+
+#include "base/callback.h"
+#include "base/time.h"
+
+namespace gfx {
+class Rect;
+class Size;
+}  // namespace gfx
+
+namespace media {
+class VideoFrame;
+}  // namespace media
+
+namespace content {
+
+// Defines an interface for listening to events of frame presentation and to
+// instruct the platform layer (i.e. RenderWidgetHostViewPort) to copy a frame.
+//
+// Further processing is possible (e.g. scale and color space conversion)
+// through this interface. See ShouldCaptureFrame() for details.
+//
+// It is platform dependent which thread this object lives on, but it is
+// guaranteed to be used on a single thread.
+class RenderWidgetHostViewFrameSubscriber {
+ public:
+  virtual ~RenderWidgetHostViewFrameSubscriber() {}
+
+  // Called when a captured frame is available or the frame is no longer
+  // needed by the platform layer.
+  //
+  // If |frame_captured| is true then frame provided contains valid content and
+  // |timestamp| is the time when the frame was painted.
+  //
+  // If |frame_captured| is false then the content in frame provided is
+  // invalid. There was an error during the process of frame capture or the
+  // platform layer is shutting down. |timestamp| is also invalid in this case.
+  typedef base::Callback<void(
+      base::Time /* timestamp */,
+      bool /* frame_captured */)> DeliverFrameCallback;
+
+  // Called when a new frame is going to be presented. Implementation can
+  // decide whether the current frame should be captured or not.
+  //
+  // Return true if the current frame should be captured. If so, |storage|
+  // should will be set to hold an appropriately sized and allocated buffer
+  // into which to copy the frame. The platform presenter will perform scaling
+  // and color space conversion to fit into the output frame.
+  //
+  // Destination format is determined by |storage|, currently only
+  // media::VideoFrame::YV12 is supported. Platform layer will perform color
+  // space conversion if needed.
+  //
+  // When the frame is available |callback| will be called. It is up to the
+  // platform layer to decide when to deliver a captured frame.
+  //
+  // Return false if the current frame should not be captured.
+  virtual bool ShouldCaptureFrame(
+      scoped_refptr<media::VideoFrame>* storage,
+      DeliverFrameCallback* callback) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PORT_BROWSER_RENDER_WIDGET_HOST_VIEW_FRAME_SUBSCRIBER_H_