Reland main thread position sticky implementation.

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

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 117 matching lines @@
     , m_inSynchronousPostLayout(false)
     , m_postLayoutTasksTimer(this, &FrameView::postLayoutTimerFired)
     , m_updateWidgetsTimer(this, &FrameView::updateWidgetsTimerFired)
     , m_renderThrottlingObserverNotificationFactory(CancellableTaskFactory::create(this, &FrameView::notifyRenderThrottlingObservers))
     , m_isTransparent(false)
     , m_baseBackgroundColor(Color::white)
     , m_mediaType(MediaTypeNames::screen)
     , m_safeToPropagateScrollToParent(true)
     , m_isTrackingPaintInvalidations(false)
     , m_scrollCorner(nullptr)
+    , m_stickyPositionObjectCount(0)
     , m_inputEventsScaleFactorForEmulation(1)
     , m_layoutSizeFixedToFrameSize(true)
     , m_didScrollTimer(this, &FrameView::didScrollTimerFired)
     , m_topControlsViewportAdjustment(0)
     , m_needsUpdateWidgetGeometries(false)
     , m_needsUpdateViewportIntersection(true)
     , m_needsUpdateViewportIntersectionInSubtree(true)
 #if ENABLE(ASSERT)
     , m_hasBeenDisposed(false)
 #endif
@@ skipping 1458 matching lines @@
 }
 
 void FrameView::updateLayersAndCompositingAfterScrollIfNeeded()
 {
     // Nothing to do after scrolling if there are no fixed position elements.
     if (!hasViewportConstrainedObjects())
         return;
 
     RawPtr<FrameView> protect(this);
 
+    // Update sticky position objects which are stuck to the viewport.
+    for (const auto& viewportConstrainedObject : *m_viewportConstrainedObjects) {
+        LayoutObject* layoutObject = viewportConstrainedObject;
+        PaintLayer* layer = toLayoutBoxModelObject(layoutObject)->layer();
+        if (layoutObject->style()->position() == StickyPosition)
+            layer->updateLayerPosition();
+    }
+
     // If there fixed position elements, scrolling may cause compositing layers to change.
     // Update widget and layer positions after scrolling, but only if we're not inside of
     // layout.
     if (!m_nestedLayoutCount) {
         updateWidgetGeometries();
         if (LayoutView* layoutView = this->layoutView())
             layoutView->layer()->setNeedsCompositingInputsUpdate();
     }
 }
 
@@ skipping 2466 matching lines @@
     return m_hiddenForThrottling && m_crossOriginForThrottling;
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink