[LayoutNG] Paint multicol container outlines correctly.

Introducing NGPhysicalFragment::IsCSSBox(), to distinguish between
fragments generated from CSS boxes [1] and those generated by the layout
engine to hold CSS box fragments. We have a lot of checks for fragments
not being line boxes before working on the associated LayoutObject, but
we need to do the same for column boxes. This CL only changes
HasLayer(), to fix outline painting, but we could do the same for many
of the other methods here.

Column boxes don't establish layers, so return false. The layout object
that a column box is associated with does establish a layer (for legacy
reasons). The outline code [2] has special-code for layers, but
shouldn't treat each column as establishing a layer.

While we wait for NG column painting to be implemented, we now need to
guard against entering columns when painting a box fragment, and instead
let the paint layer established by the multicol container and the flow
thread drive the painting (like before).

[1] https://www.w3.org/TR/css-display-3/#box-tree
[2] NGPhysicalContainerFragment::AddOutlineRectsForDescendant()

Change-Id: I6fcd753cbed2e5f19560eddf45e903dd58bf4bef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1912713Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715395}

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

@@ -273,10 +273,6 @@ Node* NGPhysicalFragment::GetNode() const {
   return !IsLineBox() ? layout_object_.GetNode() : nullptr;
 }
 
-bool NGPhysicalFragment::HasLayer() const {
-  return !IsLineBox() && layout_object_.HasLayer();
-}
-
 PaintLayer* NGPhysicalFragment::Layer() const {
   if (!HasLayer())
     return nullptr;

third_party/blink/renderer/core/layout/ng/ng_physical_fragment.h

@@ -122,6 +122,19 @@ class CORE_EXPORT NGPhysicalFragment
   bool IsFloatingOrOutOfFlowPositioned() const {
     return IsFloating() || IsOutOfFlowPositioned();
   }
+
+  // Return true if this fragment corresponds directly to an entry in the CSS
+  // box tree [1]. Note that anonymous blocks also exist in the CSS box
+  // tree. Returns false otherwise, i.e. if the fragment is generated by the
+  // layout engine to contain fragments from CSS boxes (a line or a generated
+  // fragmentainer [2], in other words). The main signification of this is
+  // whether we can use the LayoutObject associated with this fragment for all
+  // purposes.
+  //
+  // [1] https://www.w3.org/TR/css-display-3/#box-tree
+  // [2] https://www.w3.org/TR/css-break-3/#fragmentation-container
+  bool IsCSSBox() const { return !IsLineBox() && !IsColumnBox(); }
+
   bool IsBlockFlow() const;
   bool IsListMarker() const;
 
@@ -176,7 +189,7 @@ class CORE_EXPORT NGPhysicalFragment
   Node* GetNode() const;
 
   // Whether there is a PaintLayer associated with the fragment.
-  bool HasLayer() const;
+  bool HasLayer() const { return IsCSSBox() && layout_object_.HasLayer(); }
 
   // The PaintLayer associated with the fragment.
   PaintLayer* Layer() const;

third_party/blink/renderer/core/paint/ng/ng_box_fragment_painter.cc

@@ -495,7 +495,8 @@ void NGBoxFragmentPainter::PaintBlockChildren(const PaintInfo& paint_info) {
   PaintInfo paint_info_for_descendants = paint_info.ForDescendants();
   for (const NGLink& child : box_fragment_.Children()) {
     const NGPhysicalFragment& child_fragment = *child;
-    if (child_fragment.HasSelfPaintingLayer() || child_fragment.IsFloating())
+    if (child_fragment.HasSelfPaintingLayer() || child_fragment.IsFloating() ||
+        child_fragment.IsColumnBox())
       continue;
 
     if (child_fragment.Type() == NGPhysicalFragment::kFragmentBox) {
@@ -537,7 +538,7 @@ void NGBoxFragmentPainter::PaintFloatingChildren(
     const PaintInfo& float_paint_info) {
   for (const NGLink& child : container.Children()) {
     const NGPhysicalFragment& child_fragment = *child;
-    if (child_fragment.HasSelfPaintingLayer())
+    if (child_fragment.HasSelfPaintingLayer() || child_fragment.IsColumnBox())
       continue;
 
     // Atomic-inlines paint atomically, and shouldn't be traversed.

third_party/blink/web_tests/TestExpectations

@@ -1133,7 +1133,6 @@ crbug.com/954171 virtual/layout_ng_block_frag/fast/multicol/float-with-margin-mo
 crbug.com/954171 virtual/layout_ng_block_frag/fast/multicol/float-with-margin-moved-by-child-line-and-unbreakable.html [ Failure Crash ]
 crbug.com/954171 virtual/layout_ng_block_frag/fast/multicol/float-with-margin-moved-by-child-line.html [ Failure Crash ]
 crbug.com/591099 virtual/layout_ng_block_frag/fast/multicol/float-with-margin-moved-unbreakable.html [ Failure ]
-crbug.com/829028 virtual/layout_ng_block_frag/fast/multicol/focus-outline.html [ Failure ]
 crbug.com/591099 virtual/layout_ng_block_frag/fast/multicol/forced-break-after-block-with-spanner.html [ Failure ]
 crbug.com/591099 virtual/layout_ng_block_frag/fast/multicol/forced-break-after-empty-block-after-spanner.html [ Failure ]
 crbug.com/591099 virtual/layout_ng_block_frag/fast/multicol/forced-break-after-last-block-before-spanner.html [ Failure ]