Basic ScrollTimeline implementation for Animation Worklet

third_party/WebKit/Source/core/animation/ScrollTimeline.h

+// Copyright 2017 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 ScrollTimeline_h
+#define ScrollTimeline_h
+
+#include "core/CoreExport.h"
+#include "core/animation/AnimationTimeline.h"
+#include "core/animation/ScrollTimelineOptions.h"
+#include "core/dom/Element.h"
+#include "platform/bindings/ScriptWrappable.h"
+#include "platform/wtf/text/WTFString.h"
+
+namespace blink {
+
+class CORE_EXPORT ScrollTimeline final : public AnimationTimeline {
+  DEFINE_WRAPPERTYPEINFO();
+
+ public:
+  enum ScrollDirection {
+    Block,
+    Inline,
+  };
+
+  static ScrollTimeline* Create(Document&,
+                                ScrollTimelineOptions,
+                                ExceptionState&);
+
+  // AnimationTimeline overrides.
+  // TODO(smcgruer): We shouldn't have to override this many methods. Instead,
+  // DocumentTimeline should own the |CurrentTimeInternal| methods so that we
+  // only have to override |currentTime|.

[alancutter (OOO until 2018), 2017/06/08 05:00:31]

I agree with this for all the code in AnimationTimeline. It was written before
the idea of a separate DocumentTimeline interface existed, as a result the code
is really DocumentTimeline code and probably doesn't make sense to share with
ScrollTimeline. I'm not comfortable with that code getting inherited by
ScrollTimeline without necessity or test coverage, please reduce
AnimationTimeline to the bare minimum that ScrollTimeline requires before
inheriting from it.

Please let me know if this change is non-trivial.

+  double currentTime(bool& is_null) override;
+  double currentTime() override;
+  double CurrentTimeInternal(bool& is_null) override;
+  double CurrentTimeInternal() override;
+
+  // IDL API implementation.
+  Element* scrollSource();
+  String orientation();
+  void timeRange(DoubleOrScrollTimelineAutoKeyword&);
+
+  DECLARE_VIRTUAL_TRACE();
+
+ private:
+  ScrollTimeline(const Document&, Element*, ScrollDirection, double);
+
+  Member<Element> scroll_source_;
+  ScrollDirection orientation_;
+  double time_range_;
+};
+
+}  // namespace blink
+
+#endif