Add Blink support for showing image placeholders using range requests.

third_party/WebKit/Source/platform/graphics/PlaceholderImage.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 PlaceholderImage_h
+#define PlaceholderImage_h
+
+#include "platform/geometry/IntSize.h"
+#include "platform/graphics/Image.h"
+#include "platform/graphics/ImageOrientation.h"
+#include "third_party/skia/include/core/SkRefCnt.h"
+#include "wtf/PassRefPtr.h"
+
+class SkCanvas;
+class SkImage;
+class SkPaint;
+
+namespace blink {
+
+class FloatPoint;
+class FloatRect;
+class FloatSize;
+class GraphicsContext;
+class ImageObserver;
+
+// A generated placeholder image that shows a translucent gray rectangle.
+class PLATFORM_EXPORT PlaceholderImage final : public Image {
+ public:
+  static PassRefPtr<PlaceholderImage> create(ImageObserver* observer,
+                                             const IntSize& size) {
+    return adoptRef(new PlaceholderImage(observer, size));
+  }
+
+  ~PlaceholderImage() override;
+
+  IntSize size() const override { return m_size; }
+
+  sk_sp<SkImage> imageForCurrentFrame() override;
+
+  void draw(SkCanvas*,
+            const SkPaint&,
+            const FloatRect& destRect,
+            const FloatRect& srcRect,
+            RespectImageOrientationEnum,
+            ImageClampingMode) override;
+
+  void drawPattern(GraphicsContext&,
+                   const FloatRect& srcRect,
+                   const FloatSize& scale,
+                   const FloatPoint& phase,
+                   SkXfermode::Mode,
+                   const FloatRect& destRect,
+                   const FloatSize& repeatSpacing) override;
+
+ private:
+  PlaceholderImage(ImageObserver* observer, const IntSize& size)
+      : Image(observer), m_size(size) {}
+
+  bool currentFrameHasSingleSecurityOrigin() const override { return true; }
+
+  // There's no decoded data to worry about.
+  void destroyDecodedData() override {}
+
+  bool currentFrameKnownToBeOpaque(MetadataMode = UseCurrentMetadata) override {
+    // Placeholder images are translucent.
+    return false;
+  }
+
+  IntSize m_size;
+};
+
+}  // namespace blink
+
+#endif