[FlexNG] Merge anonymous flex-items when elements are removed.

This code is basically lifted from LayoutFlexibleBox::RemoveChild.

Bug: 845235
Change-Id: Icdda90143d896cb9678cab3cde1bfc4554471701
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1982619Reviewed-by: David Grogan <dgrogan@chromium.org>
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728109}

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

@@ -52,4 +52,31 @@ void LayoutNGFlexibleBox::UpdateBlockLayout(bool relayout_children) {
     descendant.node.UseLegacyOutOfFlowPositioning();
 }
 
+namespace {
+
+void MergeAnonymousFlexItems(LayoutObject* remove_child) {
+  // When we remove a flex item, and the previous and next siblings of the item
+  // are text nodes wrapped in anonymous flex items, the adjacent text nodes
+  // need to be merged into the same flex item.
+  LayoutObject* prev = remove_child->PreviousSibling();
+  if (!prev || !prev->IsAnonymousBlock())
+    return;
+  LayoutObject* next = remove_child->NextSibling();
+  if (!next || !next->IsAnonymousBlock())
+    return;
+  ToLayoutBoxModelObject(next)->MoveAllChildrenTo(ToLayoutBoxModelObject(prev));
+  To<LayoutBlockFlow>(next)->DeleteLineBoxTree();
+  next->Destroy();
+}
+
+}  // namespace
+
+void LayoutNGFlexibleBox::RemoveChild(LayoutObject* child) {
+  if (!DocumentBeingDestroyed() &&
+      !StyleRef().IsDeprecatedFlexboxUsingFlexLayout())
+    MergeAnonymousFlexItems(child);
+
+  LayoutBlock::RemoveChild(child);
+}
+
 }  // namespace blink

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

@@ -25,6 +25,8 @@ class CORE_EXPORT LayoutNGFlexibleBox : public LayoutNGMixin<LayoutBlock> {
   const char* GetName() const override { return "LayoutNGFlexibleBox"; }
 
  protected:
+  void RemoveChild(LayoutObject*) override;
+
   bool IsOfType(LayoutObjectType type) const override {
     return type == kLayoutObjectNGFlexibleBox ||
            LayoutNGMixin<LayoutBlock>::IsOfType(type);

third_party/blink/web_tests/TestExpectations

@@ -1317,8 +1317,6 @@ crbug.com/591099 virtual/layout_ng_flex_box/css3/flexbox/relpos-with-percentage-
 ### virtual/layout_ng_flex_box/external/wpt/css/css-flexbox/
 crbug.com/591099 virtual/layout_ng_flex_box/external/wpt/css/css-flexbox/align-items-004.htm [ Failure ]
 crbug.com/591099 virtual/layout_ng_flex_box/external/wpt/css/css-flexbox/align-items-baseline-overflow-non-visible.html [ Failure ]
-crbug.com/591099 virtual/layout_ng_flex_box/external/wpt/css/css-flexbox/anonymous-flex-item-001.html [ Failure ]
-crbug.com/591099 virtual/layout_ng_flex_box/external/wpt/css/css-flexbox/anonymous-flex-item-003.html [ Failure ]
 crbug.com/807497 virtual/layout_ng_flex_box/external/wpt/css/css-flexbox/anonymous-flex-item-005.html [ Failure ]
 crbug.com/591099 virtual/layout_ng_flex_box/external/wpt/css/css-flexbox/flex-basis-010.html [ Failure ]
 crbug.com/249112 virtual/layout_ng_flex_box/external/wpt/css/css-flexbox/flex-minimum-height-flex-items-005.xht [ Failure ]