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() {}
+
+void SmoothScrollSequencer::QueueAnimation(ScrollableArea* scrollable,
+                                           ScrollOffset offset) {
+  ScrollerAndOffsetPair scroller_offset(scrollable, offset);
+  queue_.push_back(scroller_offset);
+}
+
+void SmoothScrollSequencer::RunQueuedAnimations() {
+  if (queue_.IsEmpty()) {
+    current_scrollable_ = nullptr;
+    return;
+  }
+  ScrollerAndOffsetPair scroller_offset = queue_.back();
+  queue_.pop_back();
+  ScrollableArea* scrollable = scroller_offset.first;
+  current_scrollable_ = scrollable;
+  ScrollOffset offset = scroller_offset.second;
+  scrollable->SetScrollOffset(offset, kSequencedSmoothScroll,
+                              kScrollBehaviorSmooth);
+}
+
+void SmoothScrollSequencer::AbortAnimations() {
+  if (current_scrollable_) {
+    current_scrollable_->CancelProgrammaticScrollAnimation();
+    current_scrollable_ = nullptr;
+  }
+  queue_.clear();
+}
+
+DEFINE_TRACE(SmoothScrollSequencer) {
+  visitor->Trace(queue_);
+  visitor->Trace(current_scrollable_);
+}
+
+}  // namespace blink