[RootLayerScrolling] Fix position:sticky

If there are any non-composited position:sticky objects that stick
to the root layer, then we must force main thread scrolling to
prevent an "over-scrolling" effect.

BUG=711468
R=skobes@chromium.org,pdr@chromium.org,bokan@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2;master.tryserver.chromium.linux:linux_layout_tests_root_layer_scrolls
Change-Id: I4c36eaf118b8d4d0078c4d5c5e8b633eb71fe733
Reviewed-on: https://chromium-review.googlesource.com/797221
Commit-Queue: Stefan Zager <szager@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520807}

third_party/WebKit/LayoutTests/FlagExpectations/root-layer-scrolls

@@ -4,9 +4,6 @@ crbug.com/417782 compositing/squashing/dont-squash-into-videos.html [ Failure ]
 crbug.com/417782 compositing/squashing/squash-above-fixed-1.html [ Failure ]
 crbug.com/417782 compositing/squashing/squash-above-fixed-3.html [ Failure ]
 crbug.com/417782 compositing/visibility/visibility-image-layers-dynamic.html [ Failure ]
-crbug.com/417782 external/wpt/css/css-position/position-sticky-root-scroller.html [ Failure ]
-crbug.com/417782 fast/css/sticky/replaced-sticky.html [ Failure ]
-crbug.com/417782 fast/css/sticky/sticky-style-change.html [ Failure ]
 crbug.com/417782 fast/dom/Window/window-xy-properties.html [ Failure ]
 crbug.com/417782 [ Linux Mac ] fast/dom/horizontal-scrollbar-when-dir-change.html [ Failure ]
 crbug.com/417782 fast/dom/rtl-scroll-to-leftmost-and-resize.html [ Failure ]

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

@@ -5446,32 +5446,11 @@ int LocalFrameView::InitialViewportHeight() const {
 bool LocalFrameView::HasVisibleSlowRepaintViewportConstrainedObjects() const {
   if (!ViewportConstrainedObjects())
     return false;
-
   for (const LayoutObject* layout_object : *ViewportConstrainedObjects()) {
     DCHECK(layout_object->IsBoxModelObject() && layout_object->HasLayer());
     DCHECK(layout_object->Style()->GetPosition() == EPosition::kFixed ||
            layout_object->Style()->GetPosition() == EPosition::kSticky);
-    PaintLayer* layer = ToLayoutBoxModelObject(layout_object)->Layer();
-
-    // Whether the Layer sticks to the viewport is a tree-depenent
-    // property and our viewportConstrainedObjects collection is maintained
-    // with only LayoutObject-level information.
-    if (!layer->FixedToViewport() && !layer->SticksToScroller())
-      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
-    // for invisible content.
-    if (layer->SubtreeIsInvisible())
-      continue;
-
-    // We're only smart enough to scroll viewport-constrainted objects
-    // in the compositor if they have their own backing or they paint
-    // into a grouped back (which necessarily all have the same viewport
-    // constraints).
-    CompositingState compositing_state = layer->GetCompositingState();
-    if (compositing_state != kPaintsIntoOwnBacking &&
-        compositing_state != kPaintsIntoGroupedBacking)
+    if (ToLayoutBoxModelObject(layout_object)->IsSlowRepaintConstrainedObject())
       return true;
   }
   return false;

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

@@ -843,7 +843,8 @@ void LayoutBoxModelObject::UpdateStickyPositionConstraints() const {
                       .BoundingBox()
                       .Location());
   LayoutBox* scroll_ancestor =
-      Layer()->AncestorOverflowLayer()->IsRootLayer()
+      Layer()->AncestorOverflowLayer()->IsRootLayer() &&
+              !RuntimeEnabledFeatures::RootLayerScrollingEnabled()
           ? nullptr
           : &ToLayoutBox(Layer()->AncestorOverflowLayer()->GetLayoutObject());
 
@@ -1022,9 +1023,40 @@ void LayoutBoxModelObject::UpdateStickyPositionConstraints() const {
   scrollable_area->GetStickyConstraintsMap().Set(Layer(), constraints);
 }
 
+bool LayoutBoxModelObject::IsSlowRepaintConstrainedObject() const {
+  if (!HasLayer() || (Style()->GetPosition() != EPosition::kFixed &&
+                      Style()->GetPosition() != EPosition::kSticky)) {
+    return false;
+  }
+
+  PaintLayer* layer = Layer();
+
+  // Whether the Layer sticks to the viewport is a tree-depenent
+  // property and our viewportConstrainedObjects collection is maintained
+  // with only LayoutObject-level information.
+  if (!layer->FixedToViewport() && !layer->SticksToScroller())
+    return false;
+
+  // If the whole subtree is invisible, there's no reason to scroll on
+  // the main thread because we don't need to generate invalidations
+  // for invisible content.
+  if (layer->SubtreeIsInvisible())
+    return false;
+
+  // We're only smart enough to scroll viewport-constrainted objects
+  // in the compositor if they have their own backing or they paint
+  // into a grouped back (which necessarily all have the same viewport
+  // constraints).
+  return (layer->GetCompositingState() == kNotComposited);
+}
+
 FloatRect LayoutBoxModelObject::ComputeStickyConstrainingRect() const {
-  if (Layer()->AncestorOverflowLayer()->IsRootLayer())
-    return View()->GetFrameView()->VisibleContentRect();
+  if (Layer()->AncestorOverflowLayer()->IsRootLayer()) {
+    return View()
+        ->GetFrameView()
+        ->LayoutViewportScrollableArea()
+        ->VisibleContentRect();
+  }
 
   LayoutBox* enclosing_clipping_box =
       Layer()->AncestorOverflowLayer()->GetLayoutBox();

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.h

@@ -145,6 +145,7 @@ class CORE_EXPORT LayoutBoxModelObject : public LayoutObject {
   FloatRect ComputeStickyConstrainingRect() const;
   void UpdateStickyPositionConstraints() const;
   LayoutSize StickyPositionOffset() const;
+  bool IsSlowRepaintConstrainedObject() const;
 
   LayoutSize OffsetForInFlowPosition() const;
 

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

@@ -548,6 +548,7 @@ void PaintLayerScrollableArea::InvalidatePaintForScrollOffsetChange(
       if (!frame_view->InvalidateViewportConstrainedObjects())
         requires_paint_invalidation = true;
     }
+    InvalidatePaintForStickyDescendants();
   }
 
   if (requires_paint_invalidation)
@@ -1737,6 +1738,25 @@ void PaintLayerScrollableArea::InvalidateStickyConstraintsFor(
   }
 }
 
+bool PaintLayerScrollableArea::HasNonCompositedStickyDescendants() const {
+  if (const PaintLayerScrollableAreaRareData* d = RareData()) {
+    for (const PaintLayer* sticky_layer : d->sticky_constraints_map_.Keys()) {
+      if (sticky_layer->GetLayoutObject().IsSlowRepaintConstrainedObject())
+        return true;
+    }
+  }
+  return false;
+}
+
+void PaintLayerScrollableArea::InvalidatePaintForStickyDescendants() {
+  if (PaintLayerScrollableAreaRareData* d = RareData()) {
+    for (PaintLayer* sticky_layer : d->sticky_constraints_map_.Keys()) {
+      sticky_layer->GetLayoutObject()
+          .SetShouldDoFullPaintInvalidationIncludingNonCompositingDescendants();
+    }
+  }
+}
+
 IntSize PaintLayerScrollableArea::OffsetFromResizeCorner(
     const IntPoint& absolute_point) const {
   // Currently the resize corner is either the bottom right corner or the bottom
@@ -1981,6 +2001,8 @@ bool PaintLayerScrollableArea::ShouldScrollOnMainThread() const {
     if (frame->View()->GetMainThreadScrollingReasons())
       return true;
   }
+  if (HasNonCompositedStickyDescendants())
+    return true;
   return ScrollableArea::ShouldScrollOnMainThread();
 }
 

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

@@ -482,6 +482,8 @@ class CORE_EXPORT PaintLayerScrollableArea final
   void InvalidateAllStickyConstraints();
   void InvalidateStickyConstraintsFor(PaintLayer*,
                                       bool needs_compositing_update = true);
+  void InvalidatePaintForStickyDescendants();
+  bool HasNonCompositedStickyDescendants() const;
   uint32_t GetNonCompositedMainThreadScrollingReasons() {
     return non_composited_main_thread_scrolling_reasons_;
   }
@@ -546,6 +548,9 @@ class CORE_EXPORT PaintLayerScrollableArea final
   ScrollingCoordinator* GetScrollingCoordinator() const;
 
   PaintLayerScrollableAreaRareData* RareData() { return rare_data_.get(); }
+  const PaintLayerScrollableAreaRareData* RareData() const {
+    return rare_data_.get();
+  }
 
   PaintLayerScrollableAreaRareData& EnsureRareData() {
     if (!rare_data_)