Let LayoutSelection visit children of display:content element.

We stopped traversal flat tree when Node didn't have a LayoutObject
but Slot elements appear in the tree w/o LayoutObject.
This patch enables LayoutSelection to visit children of
such elements.

Bug: 870734
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: Id4f7c135fceead131f37485ecb8fa326834d72c3
Reviewed-on: https://chromium-review.googlesource.com/1164724Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581825}

third_party/blink/renderer/core/editing/layout_selection.cc

@@ -22,6 +22,7 @@
 #include "third_party/blink/renderer/core/editing/layout_selection.h"
 
 #include "third_party/blink/renderer/core/dom/document.h"
+#include "third_party/blink/renderer/core/dom/node_computed_style.h"
 #include "third_party/blink/renderer/core/editing/editing_utilities.h"
 #include "third_party/blink/renderer/core/editing/ephemeral_range.h"
 #include "third_party/blink/renderer/core/editing/frame_selection.h"
@@ -293,19 +294,30 @@ static LayoutTextFragment* FirstLetterPartFor(
   return nullptr;
 }
 
+static bool IsDisplayContentElement(const Node& node) {
+  if (!node.IsElementNode())
+    return false;
+  const ComputedStyle* const style = node.GetComputedStyle();
+  return style && style->Display() == EDisplay::kContents;
+}
+
 template <typename Visitor>
 static void VisitSelectedInclusiveDescendantsOfInternal(const Node& node,
                                                         Visitor* visitor) {
-  LayoutObject* layout_object = node.GetLayoutObject();
-  if (!layout_object)
-    return;
-  if (LayoutTextFragment* first_letter = FirstLetterPartFor(layout_object)) {
-    if (first_letter->GetSelectionState() != SelectionState::kNone)
-      visitor->Visit(first_letter);
+  // Display:content element appears in a flat tree even it doesn't have
+  // a LayoutObject but we need to visit its children.
+  if (!IsDisplayContentElement(node)) {
+    LayoutObject* layout_object = node.GetLayoutObject();
+    if (!layout_object)
+      return;
+    if (LayoutTextFragment* first_letter = FirstLetterPartFor(layout_object)) {
+      if (first_letter->GetSelectionState() != SelectionState::kNone)
+        visitor->Visit(first_letter);
+    }
+    if (layout_object->GetSelectionState() == SelectionState::kNone)
+      return;
+    visitor->Visit(layout_object);
   }
-  if (layout_object->GetSelectionState() == SelectionState::kNone)
-    return;
-  visitor->Visit(layout_object);
 
   for (Node& child : FlatTreeTraversal::ChildrenOf(node))
     VisitSelectedInclusiveDescendantsOfInternal(child, visitor);

third_party/blink/renderer/core/editing/layout_selection_test.cc

@@ -850,6 +850,35 @@ TEST_F(LayoutSelectionTest, MoveNode) {
       DumpSelectionInfo());
 }
 
+// http://crbug.com/870734
+TEST_F(LayoutSelectionTest, InvalidateSlot) {
+  Selection().SetSelectionAndEndTyping(
+      SetSelectionTextToBody("^<div>"
+                             "<template data-mode=open>"
+                             "<slot></slot>"
+                             "</template>"
+                             "foo"
+                             "</div>|"));
+  UpdateAllLifecyclePhases();
+  EXPECT_EQ(
+      "BODY, Contain, NotInvalidate \n"
+      "  DIV, Contain, NotInvalidate \n"
+      "    #shadow-root \n"
+      "      SLOT, <null LayoutObject> \n"
+      "    'foo', StartAndEnd, NotInvalidate ",
+      DumpSelectionInfo());
+
+  Selection().Clear();
+  Selection().CommitAppearanceIfNeeded();
+  EXPECT_EQ(
+      "BODY, None, NotInvalidate \n"
+      "  DIV, None, NotInvalidate \n"
+      "    #shadow-root \n"
+      "      SLOT, <null LayoutObject> \n"
+      "    'foo', None, ShouldInvalidate ",
+      DumpSelectionInfo());
+}
+
 static const NGPaintFragment* FindNGPaintFragmentInternal(
     const NGPaintFragment* paint,
     const LayoutObject* layout_object) {