Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 976 matching lines @@
 #endif
 
 bool ScrollingCoordinator::hasVisibleSlowRepaintViewportConstrainedObjects(FrameView* frameView) const
 {
     const FrameView::ViewportConstrainedObjectSet* viewportConstrainedObjects = frameView->viewportConstrainedObjects();
     if (!viewportConstrainedObjects)
         return false;
 
     for (const LayoutObject* layoutObject : *viewportConstrainedObjects) {
         ASSERT(layoutObject->isBoxModelObject() && layoutObject->hasLayer());
-        ASSERT(layoutObject->style()->position() == FixedPosition);
+        ASSERT(layoutObject->style()->position() == FixedPosition
+            || layoutObject->style()->position() == StickyPosition);
         PaintLayer* layer = toLayoutBoxModelObject(layoutObject)->layer();
 
         // Whether the Layer scrolls with the viewport is a tree-depenent
         // property and our viewportConstrainedObjects collection is maintained
         // with only LayoutObject-level information.
         if (!layer->scrollsWithViewport())
             continue;
 
         // If the whole subtree is invisible, there's no reason to scroll on
         // the main thread because we don't need to generate invalidations
@@ skipping 20 matching lines @@
         reasons |= ThreadedScrollingDisabled;
 
     if (!m_page->mainFrame()->isLocalFrame())
         return reasons;
     FrameView* frameView = m_page->deprecatedLocalMainFrame()->view();
     if (!frameView)
         return reasons;
 
     if (frameView->hasBackgroundAttachmentFixedObjects())
         reasons |= HasBackgroundAttachmentFixedObjects;
+    if (frameView->hasStickyPositionObjects())
+        reasons |= HasStickyPositionObjects;
     FrameView::ScrollingReasons scrollingReasons = frameView->scrollingReasons();
     const bool mayBeScrolledByInput = (scrollingReasons == FrameView::Scrollable);
     const bool mayBeScrolledByScript = mayBeScrolledByInput || (scrollingReasons ==
         FrameView::NotScrollableExplicitlyDisabled);
 
     // TODO(awoloszyn) Currently crbug.com/304810 will let certain
     // overflow:hidden elements scroll on the compositor thread, so we should
     // not let this move there path as an optimization, when we have slow-repaint
     // elements.
     if (mayBeScrolledByScript && hasVisibleSlowRepaintViewportConstrainedObjects(frameView)) {
         reasons |= HasNonLayerViewportConstrainedObjects;
     }
 
     return reasons;
 }
 
 String ScrollingCoordinator::mainThreadScrollingReasonsAsText(MainThreadScrollingReasons reasons)
 {
     StringBuilder stringBuilder;
 
     if (reasons & ScrollingCoordinator::HasBackgroundAttachmentFixedObjects)
         stringBuilder.appendLiteral("Has background-attachment:fixed, ");
     if (reasons & ScrollingCoordinator::HasNonLayerViewportConstrainedObjects)
         stringBuilder.appendLiteral("Has non-layer viewport-constrained objects, ");
+    if (reasons & ScrollingCoordinator::HasStickyPositionObjects)
+        stringBuilder.appendLiteral("Has sticky position objects, ");
     if (reasons & ScrollingCoordinator::ThreadedScrollingDisabled)
         stringBuilder.appendLiteral("Threaded scrolling is disabled, ");
 
     if (stringBuilder.length())
         stringBuilder.resize(stringBuilder.length() - 2);
     return stringBuilder.toString();
 }
 
 String ScrollingCoordinator::mainThreadScrollingReasonsAsText() const
 {
     ASSERT(m_page->deprecatedLocalMainFrame()->document()->lifecycle().state() >= DocumentLifecycle::CompositingClean);
     return mainThreadScrollingReasonsAsText(m_lastMainThreadScrollingReasons);
 }
 
 bool ScrollingCoordinator::frameViewIsDirty() const
 {
     FrameView* frameView = m_page->mainFrame()->isLocalFrame() ? m_page->deprecatedLocalMainFrame()->view() : nullptr;
     bool frameIsScrollable = frameView && frameView->isScrollable();
     if (frameIsScrollable != m_wasFrameScrollable)
         return true;
 
     if (WebLayer* scrollLayer = frameView ? toWebLayer(frameView->layerForScrolling()) : nullptr)
         return WebSize(frameView->contentsSize()) != scrollLayer->bounds();
     return false;
 }
 
 } // namespace blink