Implement Element.scrollIntoView for scroll-behavior: smooth.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 894d81f85ace408237a9936f9ac218ecd574e509..1516037a006f1eff66f90dc7b7e79d91d90cefbf 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -211,6 +211,13 @@ HostWindow* PaintLayerScrollableArea::getHostWindow() const {
   return nullptr;
 }
 
+ProgrammaticScrollCoordinator*
+PaintLayerScrollableArea::getProgrammaticScrollCoordinator() const {
+  if (Page* page = box().frame()->page())
+    return page->scrollingCoordinator()->programmaticScrollCoordinator();
+  return nullptr;
+}
+
 GraphicsLayer* PaintLayerScrollableArea::layerForScrolling() const {
   return layer()->hasCompositedLayerMapping()
              ? layer()->compositedLayerMapping()->scrollingContentsLayer()
@@ -1630,7 +1637,8 @@ LayoutRect PaintLayerScrollableArea::scrollIntoView(
     const LayoutRect& rect,
     const ScrollAlignment& alignX,
     const ScrollAlignment& alignY,
-    ScrollType scrollType) {
+    ScrollType scrollType,
+    ScrollBehavior scrollBehavior) {
   LayoutRect localExposeRect(
       box()
           .absoluteToLocalQuad(FloatQuad(FloatRect(rect)), UseTransforms)
@@ -1644,7 +1652,12 @@ LayoutRect PaintLayerScrollableArea::scrollIntoView(
   ScrollOffset oldScrollOffset = getScrollOffset();
   ScrollOffset newScrollOffset(clampScrollOffset(roundedIntSize(
       toScrollOffset(FloatPoint(r.location()) + oldScrollOffset))));
-  setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
+  if (scrollType == ProgrammaticScroll &&
+      scrollBehavior == ScrollBehaviorSmooth) {
+    getProgrammaticScrollCoordinator()->queueAnimation(this, newScrollOffset);

[bokan, 2017/02/02 22:51:50]

Hmm, maybe I'm missing something obvious here, but why do we need this new
ProgrammaticScrollCoordinator rather than using the existing path for
Element::scrollTo that just calls setScrollOffset with smooth behavior? Is it
because scrollIntoView can cause coordinated scrolling between many boxes and we
need to a way to queue those up and play them back linearly?

[sunyunjia, 2017/02/10 23:25:20]

Right! See here:
https://docs.google.com/a/chromium.org/document/d/1EeGvVnlHjIVVKwU-Y-A4uYtB-B...

[bokan, 2017/02/21 21:33:00]

Got it. I think the name makes it sound like it's related to
ScrollingCoordinator which it isn't. I think SmoothScrollSequencer or something
similar might be better.

+  } else {
+    setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
+  }
   ScrollOffset scrollOffsetDifference = getScrollOffset() - oldScrollOffset;
   localExposeRect.move(-LayoutSize(scrollOffsetDifference));