Synchronize OffscreenCanvas content with the placeholder canvas

third_party/WebKit/Source/platform/graphics/OffscreenCanvasPlaceholder.h

+// Copyright 2016 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 OffscreenCanvasPlaceholder_h
+#define OffscreenCanvasPlaceholder_h
+
+#include "wtf/RefPtr.h"
+#include "wtf/WeakPtr.h"
+#include <memory>
+
+namespace blink {
+
+class Image;
+class OffscreenCanvasFrameDispatcher;
+class WebTaskRunner;
+
+class OffscreenCanvasPlaceholder {
+ public:
+  ~OffscreenCanvasPlaceholder();
+
+  void setPlaceholderFrame(RefPtr<Image>,
+                           WeakPtr<OffscreenCanvasFrameDispatcher>,
+                           std::unique_ptr<WebTaskRunner>,
+                           unsigned resourceId);
+  void releasePlaceholderFrame();
+
+  static OffscreenCanvasPlaceholder* getPlaceholderById(unsigned placeholderId);
+
+  void registerPlaceholder(unsigned placeholderId);
+  void unregisterPlaceholder();
+  const RefPtr<Image>& placeholderFrame() const { return m_placeholderFrame; }
+
+ private:
+  bool isPlaceholderRegistered() const {
+    return m_placeholderId != kNoPlaceholderId;
+  }
+
+  RefPtr<Image> m_placeholderFrame;
+  WeakPtr<OffscreenCanvasFrameDispatcher> m_frameDispatcher;
+  std::unique_ptr<WebTaskRunner> m_frameDispatcherTaskRunner;
+  unsigned m_placeholderFrameResourceId = 0;
+
+  enum {
+    kNoPlaceholderId = -1,
+  };
+  int m_placeholderId = kNoPlaceholderId;
+};
+
+}  // blink
+
+#endif