Implement Element.scrollIntoView for scroll-behavior: smooth.

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

+// 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.
+#include "platform/scroll/SmoothScrollSequencer.h"
+
+#include "platform/scroll/ProgrammaticScrollAnimator.h"
+#include "platform/scroll/ScrollableArea.h"
+
+namespace blink {
+
+SmoothScrollSequencer* SmoothScrollSequencer::create() {
+  return new SmoothScrollSequencer();
+}
+
+SmoothScrollSequencer::SmoothScrollSequencer() {}
+
+SmoothScrollSequencer::~SmoothScrollSequencer() {}
+
+void SmoothScrollSequencer::queueAnimation(ScrollableArea* scrollable,
+                                           ScrollOffset offset) {
+  ScrollerAndOffsetPair scrollerOffset(scrollable, offset);
+  m_queue.push_back(scrollerOffset);
+}
+
+void SmoothScrollSequencer::runQueuedAnimations() {
+  if (!m_queue.empty()) {
+    ScrollerAndOffsetPair scrollerOffset = m_queue.back();
+    ScrollableArea* scrollable = scrollerOffset.first;
+    ScrollOffset offset = scrollerOffset.second;
+    scrollable->programmaticScrollAnimator().animateToOffset(offset);

[bokan, 2017/04/07 15:56:52]

Unless I'm missing something, I think it'd be better to pop the animation when
you start it on the animator here, rather than in notifyFinished. Otherwise,
calling runQueuedAnimations repeatedly will run the same animation. If we ever
have a bug where nofityAnimationFinished isn't called, we wont just miss playing
the next animation - we'll stall the whole queue. (I just dealt with such a bug
on the CC side)

[sunyunjia, 2017/05/12 18:40:25]

Done.

+  }
+}
+
+void SmoothScrollSequencer::notifyAnimationFinished() {
+  if (!m_queue.empty()) {
+    m_queue.pop_back();
+    runQueuedAnimations();
+  }
+}
+
+void SmoothScrollSequencer::abortAnimations() {
+  m_queue.clear();
+}
+
+}  // namespace blink