Use ScrollAnchor in FrameView and PaintLayerScrollableArea.

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index c03a43da5441570cb3df102af5f03d1cedbceeb4..27fbda41b65f7107f5b55832b95d43603a0db20a 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -153,6 +153,7 @@ FrameView::FrameView(LocalFrame* frame)
     , m_hiddenForThrottling(false)
     , m_crossOriginForThrottling(false)
     , m_isUpdatingAllLifecyclePhases(false)
+    , m_scrollAnchor(this)
 {
     ASSERT(m_frame);
     init();
@@ -197,6 +198,7 @@ DEFINE_TRACE(FrameView)
     visitor->trace(m_verticalScrollbar);
     visitor->trace(m_children);
     visitor->trace(m_viewportScrollableArea);
+    visitor->trace(m_scrollAnchor);
 #endif
     Widget::trace(visitor);
     ScrollableArea::trace(visitor);
@@ -794,6 +796,9 @@ void FrameView::performPreLayoutTasks()
         ASSERT(layoutViewport);
         m_viewportScrollableArea = RootFrameViewport::create(visualViewport, *layoutViewport);
     }
+
+    if (scrollAnchoringEnabled())
+        m_scrollAnchor.save();
 }
 
 static inline void layoutFromRootObject(LayoutObject& root)
@@ -1529,6 +1534,9 @@ void FrameView::setScrollPosition(const DoublePoint& scrollPoint, ScrollType scr
         scrollBehavior = scrollBehaviorStyle();
 
     ScrollableArea::setScrollPosition(newScrollPosition, scrollType, scrollBehavior);
+
+    if (scrollAnchoringEnabled() && scrollType != AnchoringScroll)
+        m_scrollAnchor.clear();
 }
 
 void FrameView::didUpdateElasticOverscroll()
@@ -2010,6 +2018,9 @@ void FrameView::performPostLayoutTasks()
         scrollingCoordinator->notifyGeometryChanged();
 
     scrollToFragmentAnchor();
+    // TODO(skobes): Figure out interactions between scroll anchor, fragment anchor, and history restoration.
+    if (scrollAnchoringEnabled())
+        m_scrollAnchor.restore();
 
     sendResizeEventIfNeeded();
 }
@@ -4057,4 +4068,11 @@ LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
     return *layoutView();
 }
 
+bool FrameView::scrollAnchoringEnabled() const
+{
+    if (Settings* settings = frame().settings())
+        return settings->scrollAnchoringEnabled();
+    return false;
+}
+
 } // namespace blink