Update PaintLayer size during layout, not after.

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 768 matching lines @@
       child_has3d = true;
 
     if (child_has3d) {
       has3d_transformed_descendant_ = true;
       break;
     }
   }
 }
 
 void PaintLayer::UpdateLayerPosition() {
+  // LayoutBoxes will call UpdateSizeAndScrollingAfterLayout() from
+  // LayoutBox::UpdateAfterLayout, but LayoutInlines will still need to update
+  // their size.
+  if (GetLayoutObject().IsInline() && GetLayoutObject().IsLayoutInline())
+    UpdateSizeAndScrollingAfterLayout();
   LayoutPoint local_point;
-
-  bool did_resize = false;
-  if (GetLayoutObject().IsInline() && GetLayoutObject().IsLayoutInline()) {
-    LayoutInline& inline_flow = ToLayoutInline(GetLayoutObject());
-    IntRect line_box = EnclosingIntRect(inline_flow.LinesBoundingBox());
-    size_ = line_box.Size();
-  } else if (LayoutBox* box = GetLayoutBox()) {
-    IntSize new_size = PixelSnappedIntSize(box->Size(), box->Location());
-    did_resize = new_size != size_;
-    size_ = new_size;
+  if (LayoutBox* box = GetLayoutBox()) {
     local_point.MoveBy(box->PhysicalLocation());
   }
 
   if (!GetLayoutObject().IsOutOfFlowPositioned() &&
       !GetLayoutObject().IsColumnSpanAll()) {
     // We must adjust our position by walking up the layout tree looking for the
     // nearest enclosing object with a layer.
     LayoutObject* curr = GetLayoutObject().Container();
     while (curr && !curr->HasLayer()) {
       if (curr->IsBox() && !curr->IsTableRow()) {
@@ skipping 30 matching lines @@
     LayoutSize new_offset = GetLayoutObject().OffsetForInFlowPosition();
     if (rare_data_ || !new_offset.IsZero())
       EnsureRareData().offset_for_in_flow_position = new_offset;
     local_point.Move(new_offset);
   } else if (rare_data_) {
     rare_data_->offset_for_in_flow_position = LayoutSize();
   }
 
   location_ = local_point;
 
-  if (scrollable_area_ && did_resize)
-    scrollable_area_->VisibleSizeChanged();
-
 #if DCHECK_IS_ON()
   needs_position_update_ = false;
 #endif
 }
 
+void PaintLayer::UpdateSizeAndScrollingAfterLayout() {
+  bool did_resize = false;
+  if (IsRootLayer() && RuntimeEnabledFeatures::rootLayerScrollingEnabled()) {
+    const IntSize new_size = GetLayoutObject().GetDocument().View()->Size();
+    did_resize = new_size != size_;
+    size_ = new_size;
+  } else if (GetLayoutObject().IsInline() &&
+             GetLayoutObject().IsLayoutInline()) {
+    LayoutInline& inline_flow = ToLayoutInline(GetLayoutObject());
+    IntRect line_box = EnclosingIntRect(inline_flow.LinesBoundingBox());
+    size_ = line_box.Size();
+  } else if (LayoutBox* box = GetLayoutBox()) {
+    IntSize new_size = PixelSnappedIntSize(box->Size(), box->Location());
+    did_resize = new_size != size_;
+    size_ = new_size;
+  }
+  if (GetLayoutObject().HasOverflowClip()) {
+    scrollable_area_->UpdateAfterLayout();
+    if (did_resize)
+      scrollable_area_->VisibleSizeChanged();
+  }
+}
+
 TransformationMatrix PaintLayer::PerspectiveTransform() const {
   if (!GetLayoutObject().HasTransformRelatedProperty())
     return TransformationMatrix();
 
   const ComputedStyle& style = GetLayoutObject().StyleRef();
   if (!style.HasPerspective())
     return TransformationMatrix();
 
   TransformationMatrix t;
   t.ApplyPerspective(style.Perspective());
@@ skipping 2448 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->EnclosingLayer());
 }
 #endif