Implement Element.scrollIntoView for scroll-behavior: smooth.

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

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
index 769acc39df44b05836e2d8ab1259afcd765a904f..0eb408c2ca75d28dd60b9d0dd1f261cf87488eae 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
@@ -37,6 +37,7 @@
 #include "platform/scroll/MainThreadScrollingReason.h"
 #include "platform/scroll/ProgrammaticScrollAnimator.h"
 #include "platform/scroll/ScrollbarTheme.h"
+#include "platform/scroll/SmoothScrollSequencer.h"
 
 static const int kPixelsPerLineStep = 40;
 static const float kMinFractionToStepWhenPaging = 0.875f;
@@ -154,6 +155,8 @@ ScrollResult ScrollableArea::UserScroll(ScrollGranularity granularity,
   }
 
   CancelProgrammaticScrollAnimation();
+  if (SmoothScrollSequencer* sequencer = GetSmoothScrollSequencer())
+    sequencer->AbortAnimations();
 
   ScrollResult result =
       GetScrollAnimator().UserScroll(granularity, pixel_delta);
@@ -170,6 +173,12 @@ ScrollResult ScrollableArea::UserScroll(ScrollGranularity granularity,
 void ScrollableArea::SetScrollOffset(const ScrollOffset& offset,
                                      ScrollType scroll_type,
                                      ScrollBehavior behavior) {
+  if (scroll_type != kSequencedSmoothScroll && scroll_type != kClampingScroll &&
+      scroll_type != kAnchoringScroll) {

[bokan, 2017/06/07 17:56:00]

just FYI: I'm not sure how anchoring scrolls should interact with this since a
scroll anchor could change the location of the thing we're trying to scroll into
view. But stopping the scroll into view doesn't sound good to me either and
trying to recalculate on the fly sounds incredibly complex for what should be an
edge case so I think  this is fine unless we find it doesn't work well in
practice.

[sunyunjia, 2017/06/07 18:34:10]

Acknowledged.

+    if (SmoothScrollSequencer* sequencer = GetSmoothScrollSequencer())
+      sequencer->AbortAnimations();
+  }
+
   ScrollOffset clamped_offset = ClampScrollOffset(offset);
   if (clamped_offset == GetScrollOffset())
     return;
@@ -187,7 +196,10 @@ void ScrollableArea::SetScrollOffset(const ScrollOffset& offset,
                                                             scroll_type);
       break;
     case kProgrammaticScroll:
-      ProgrammaticScrollHelper(clamped_offset, behavior);
+      ProgrammaticScrollHelper(clamped_offset, behavior, false);
+      break;
+    case kSequencedSmoothScroll:
+      ProgrammaticScrollHelper(clamped_offset, behavior, true);
       break;
     case kUserScroll:
       UserScrollHelper(clamped_offset, behavior);
@@ -222,19 +234,25 @@ void ScrollableArea::SetScrollOffsetSingleAxis(ScrollbarOrientation orientation,
   ScrollableArea::SetScrollOffset(new_offset, scroll_type, behavior);
 }
 
-void ScrollableArea::ProgrammaticScrollHelper(const ScrollOffset& offset,
-                                              ScrollBehavior scroll_behavior) {
+void ScrollableArea::ProgrammaticScrollHelper(
+    const ScrollOffset& offset,
+    ScrollBehavior scroll_behavior,
+    bool sequenced_for_smooth_scroll) {
   CancelScrollAnimation();
 
-  if (scroll_behavior == kScrollBehaviorSmooth)
-    GetProgrammaticScrollAnimator().AnimateToOffset(offset);
-  else
+  if (scroll_behavior == kScrollBehaviorSmooth) {
+    GetProgrammaticScrollAnimator().AnimateToOffset(
+        offset, sequenced_for_smooth_scroll);
+  } else {
     GetProgrammaticScrollAnimator().ScrollToOffsetWithoutAnimation(offset);
+  }
 }
 
 void ScrollableArea::UserScrollHelper(const ScrollOffset& offset,
                                       ScrollBehavior scroll_behavior) {
   CancelProgrammaticScrollAnimation();
+  if (SmoothScrollSequencer* sequencer = GetSmoothScrollSequencer())
+    sequencer->AbortAnimations();
 
   float x = UserInputScrollable(kHorizontalScrollbar)
                 ? offset.Width()
@@ -255,6 +273,7 @@ void ScrollableArea::UserScrollHelper(const ScrollOffset& offset,
 LayoutRect ScrollableArea::ScrollIntoView(const LayoutRect& rect_in_content,
                                           const ScrollAlignment& align_x,
                                           const ScrollAlignment& align_y,
+                                          bool is_smooth,
                                           ScrollType) {
   // TODO(bokan): This should really be implemented here but ScrollAlignment is
   // in Core which is a dependency violation.