[LayoutNG] Set IsSelfCollapsing directly from NGBlockNode.

The CheckIsSelfCollapsing code looked a little scary, e.g. for inline
children it was checking if a (legacy) linebox was was present.

This sets the self-collapsing bit directly for the layout overflow
calculation - which might have a slight perf improvement.

Change-Id: I1b214f915005b8ef21a32305be762f9d52f9156b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1556399Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682655}

third_party/blink/renderer/core/layout/layout_block_flow.cc

@@ -356,7 +356,8 @@ bool LayoutBlockFlow::IsSelfCollapsingBlock() const {
     DCHECK(CreatesNewFormattingContext());
     return false;
   }
-  DCHECK_EQ(!is_self_collapsing_, !CheckIfIsSelfCollapsingBlock());
+  if (!IsLayoutNGObject())
+    DCHECK_EQ(!is_self_collapsing_, !CheckIfIsSelfCollapsingBlock());
   return is_self_collapsing_;
 }
 
@@ -541,7 +542,7 @@ void LayoutBlockFlow::UpdateBlockLayout(bool relayout_children) {
     PositionDialog();
 
   ClearNeedsLayout();
-  UpdateIsSelfCollapsing();
+  is_self_collapsing_ = CheckIfIsSelfCollapsingBlock();
   NotifyDisplayLockDidLayout(DisplayLockContext::kSelf);
 }
 

third_party/blink/renderer/core/layout/layout_block_flow.h

@@ -443,10 +443,8 @@ class CORE_EXPORT LayoutBlockFlow : public LayoutBlock {
 
   LayoutUnit LogicalHeightWithVisibleOverflow() const final;
 
-  // This function is only public so we can call it from NGBlockNode while we're
-  // still working on LayoutNG.
-  void UpdateIsSelfCollapsing() {
-    is_self_collapsing_ = CheckIfIsSelfCollapsingBlock();
+  void SetIsSelfCollapsingFromNG(bool is_self_collapsing) {
+    is_self_collapsing_ = is_self_collapsing;
   }
 
   // These functions are only public so we can call it from NGBlockNode while

third_party/blink/renderer/core/layout/ng/ng_block_node.cc

@@ -781,7 +781,7 @@ void NGBlockNode::CopyFragmentDataToLayoutBox(
 
   // Overflow computation depends on this being set.
   if (LIKELY(block_flow))
-    block_flow->UpdateIsSelfCollapsing();
+    block_flow->SetIsSelfCollapsingFromNG(layout_result.IsSelfCollapsing());
 
   // We should notify the display lock that we've done layout on self, and if
   // it's not blocked, on children.