Implement Element.scrollIntoView for scroll-behavior: smooth.

third_party/WebKit/Source/platform/scroll/SmoothScrollSequencer.h

+// Copyright (c) 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 SmoothScrollSequencer_h
+#define SmoothScrollSequencer_h
+
+#include <utility>
+#include <vector>
+#include "platform/heap/Handle.h"
+#include "platform/scroll/ScrollTypes.h"
+
+namespace blink {
+
+class ScrollableArea;
+
+// A sequencer that stacks the nested scrollers from inside to outside,

[bokan, 2017/05/15 17:15:28]

s/stacks/queues

[sunyunjia, 2017/05/19 16:24:29]

Done.

+// so that they can be animated from outside to inside when smooth scroll
+// is called.
+class PLATFORM_EXPORT SmoothScrollSequencer
+    : public GarbageCollectedFinalized<SmoothScrollSequencer> {

[bokan, 2017/05/15 17:15:28]

This class doesn't require finalization so it should inherit from
GarbageCollected

[sunyunjia, 2017/05/19 16:24:29]

I'm not very familiar with Oilpan management, but the compiler tells me that
"Field std::vector<ScrollerAndOffsetPair> queue_ requires finalization."

[bokan, 2017/05/19 18:37:14]

Ah, we should be using HeapVector instead since we're storing handles into the
Oilpan heap. In that case, to my comment in TRACE, you only need to trace the
HeapVector and it'll do the iteration for you I think. See how this is done for
Fullscreen::fullscreen_element_stack_.

+ public:
+  static SmoothScrollSequencer* Create();
+
+  ~SmoothScrollSequencer();
+
+  // Add a scroll offset animation to the back of a queue.
+  void QueueAnimation(ScrollableArea*, ScrollOffset);
+
+  // Run the animation at the back of the queue.
+  void RunQueuedAnimations();
+
+  // Abort the currently running anmation and all the animations in the queue.

[bokan, 2017/05/15 17:15:28]

nit: typo: anmation

[sunyunjia, 2017/05/19 16:24:29]

Done.

+  void AbortAnimations();
+
+  DECLARE_TRACE();
+
+ protected:
+  SmoothScrollSequencer();
+
+ private:
+  typedef std::pair<Member<ScrollableArea>, ScrollOffset> ScrollerAndOffsetPair;
+  std::vector<ScrollerAndOffsetPair> queue_;
+  Member<ScrollableArea> current_scrollable_;
+};
+
+}  // namespace blink
+
+#endif  // SmoothScrollSequencer_h