Implement position: sticky updates on compositor

cc/layers/layer_sticky_position_constraint.h

+// Copyright 2013 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 CC_LAYERS_LAYER_STICKY_POSITION_CONSTRAINT_H_
+#define CC_LAYERS_LAYER_STICKY_POSITION_CONSTRAINT_H_
+
+#include "cc/base/cc_export.h"
+
+#include "ui/gfx/geometry/rect.h"
+
+namespace cc {
+
+namespace proto {
+class LayerStickyPositionConstraint;
+}
+
+struct CC_EXPORT LayerStickyPositionConstraint {
+  LayerStickyPositionConstraint();
+  LayerStickyPositionConstraint(const LayerStickyPositionConstraint& other);
+
+  bool is_sticky : 1;
+  bool is_anchored_left : 1;
+  bool is_anchored_right : 1;
+  bool is_anchored_top : 1;
+  bool is_anchored_bottom : 1;
+
+  // The offset from each edge of the ancestor scroller (or the viewport) to
+  // try to maintain to the sticky box as we scroll.
+  float left_offset;
+  float right_offset;
+  float top_offset;
+  float bottom_offset;
+
+  // The rectangle corresponding to original layout position of the sticky box
+  // relative to the scroll ancestor. The sticky box is only offset once the
+  // scroll has passed its initial position (e.g. top_offset will only push
+  // the element down from its original position).
+  gfx::Rect scroll_container_relative_sticky_box_rect;
+
+  // The layout rectangle of the sticky box's containing block relative to the
+  // scroll ancestor. The sticky box is only moved as far as its containing
+  // block boundary.
+  gfx::Rect scroll_container_relative_containing_block_rect;
+
+  void ToProtobuf(proto::LayerStickyPositionConstraint* proto) const;
+  void FromProtobuf(const proto::LayerStickyPositionConstraint& proto);
+
+  bool operator==(const LayerStickyPositionConstraint&) const;
+  bool operator!=(const LayerStickyPositionConstraint&) const;
+};
+
+}  // namespace cc
+
+#endif  // CC_LAYERS_LAYER_STICKY_POSITION_CONSTRAINT_H_