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 98fbad2cfa1d92d0135b8f87a218ea762d250839..be15e2992e63bdd3eafcd0a687096da44f4a096a 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);
@@ -270,6 +272,9 @@ void FrameView::dispose()
         scrollAnimator->cancelAnimation();
     cancelProgrammaticScrollAnimation();
 
+    if (RuntimeEnabledFeatures::scrollAnchoringEnabled())
+        m_scrollAnchor.clear();
+
     detachScrollbars();
 
     // When the view is no longer associated with a frame, it needs to be removed from the ax object cache
@@ -795,6 +800,9 @@ void FrameView::performPreLayoutTasks()
         ASSERT(layoutViewport);
         m_viewportScrollableArea = RootFrameViewport::create(visualViewport, *layoutViewport);
     }
+
+    if (RuntimeEnabledFeatures::scrollAnchoringEnabled())
+        m_scrollAnchor.save();
 }
 
 static inline void layoutFromRootObject(LayoutObject& root)
@@ -1534,6 +1542,9 @@ void FrameView::setScrollPosition(const DoublePoint& scrollPoint, ScrollType scr
         scrollBehavior = scrollBehaviorStyle();
 
     ScrollableArea::setScrollPosition(newScrollPosition, scrollType, scrollBehavior);
+
+    if (RuntimeEnabledFeatures::scrollAnchoringEnabled() && scrollType != AnchoringScroll)
+        m_scrollAnchor.clear();
 }
 
 void FrameView::didUpdateElasticOverscroll()
@@ -2045,6 +2056,9 @@ void FrameView::performPostLayoutTasks()
         scrollingCoordinator->notifyGeometryChanged();
 
     scrollToFragmentAnchor();
+    // TODO(skobes): Figure out interactions between scroll anchor, fragment anchor, and history restoration.
+    if (RuntimeEnabledFeatures::scrollAnchoringEnabled())
+        m_scrollAnchor.restore();
 
     sendResizeEventIfNeeded();
 }