[FragmentItem] Implement |BuildBackplate|

This patch implements |BuildBackplate| for |NGFragmentItem|.

Bug: 982194
Change-Id: I352a8edef64d3c936d34075742e42d124c1bfdbe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003150
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732329}

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

@@ -119,8 +119,8 @@ template <typename Base>
 bool LayoutNGBlockFlowMixin<
     Base>::PaintedOutputOfObjectHasNoEffectRegardlessOfSize() const {
   // LayoutNGBlockFlowMixin is in charge of paint invalidation of the first
-  // line.
-  if (PaintFragment())
+  // line and painting backplates.
+  if (PaintFragment() || Base::FragmentItems())
     return false;
 
   if (Base::StyleRef().HasColumnRule())

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

@@ -167,48 +167,75 @@ bool FragmentRequiresLegacyFallback(const NGPhysicalFragment& fragment) {
 // the paragraph level. Store the results in paragraph_backplates.
 Vector<PhysicalRect> BuildBackplate(NGInlineCursor* descendants,
                                     const PhysicalOffset& paint_offset) {
-  Vector<PhysicalRect> paragraph_backplates;
-  PhysicalRect current_backplate;
-  int consecutive_line_breaks = 0;
-
   // The number of consecutive forced breaks that split the backplate by
   // paragraph.
   static constexpr int kMaxConsecutiveLineBreaks = 2;
 
+  struct Backplates {
+    STACK_ALLOCATED();
+
+   public:
+    void AddTextRect(const PhysicalRect& box_rect) {
+      if (consecutive_line_breaks >= kMaxConsecutiveLineBreaks) {
+        // This is a paragraph point.
+        paragraph_backplates.push_back(current_backplate);
+        current_backplate = PhysicalRect();
+      }
+      consecutive_line_breaks = 0;
+
+      current_backplate.Unite(box_rect);
+    }
+
+    void AddLineBreak() { consecutive_line_breaks++; }
+
+    Vector<PhysicalRect> paragraph_backplates;
+    PhysicalRect current_backplate;
+    int consecutive_line_breaks = 0;
+  } backplates;
+
   // Build up and paint backplates of all child inline text boxes. We are not
   // able to simply use the linebox rect to compute the backplate because the
   // backplate should only be painted for inline text and not for atomic
   // inlines.
   for (; *descendants; descendants->MoveToNext()) {
-    const NGPaintFragment* child = descendants->CurrentPaintFragment();
-    if (!child)  // TODO(kojii): Support NGFragmentItem
-      continue;
+    if (const NGPaintFragment* child = descendants->CurrentPaintFragment()) {
       const NGPhysicalFragment& child_fragment = child->PhysicalFragment();
       if (child_fragment.IsHiddenForPaint() || child_fragment.IsFloating())
         continue;
       if (auto* text_fragment =
               DynamicTo<NGPhysicalTextFragment>(child_fragment)) {
         if (text_fragment->IsLineBreak()) {
-        consecutive_line_breaks++;
+          backplates.AddLineBreak();
           continue;
         }
 
-      if (consecutive_line_breaks >= kMaxConsecutiveLineBreaks) {
-        // This is a paragraph point.
-        paragraph_backplates.push_back(current_backplate);
-        current_backplate = PhysicalRect();
+        PhysicalRect box_rect(
+            child->InlineOffsetToContainerBox() + paint_offset, child->Size());
+        backplates.AddTextRect(box_rect);
+      }
+      continue;
+    }
+    if (const NGFragmentItem* child_item = descendants->CurrentItem()) {
+      if (child_item->IsHiddenForPaint())
+        continue;
+      if (child_item->IsText()) {
+        if (child_item->IsLineBreak()) {
+          backplates.AddLineBreak();
+          continue;
         }
-      consecutive_line_breaks = 0;
 
-      PhysicalRect box_rect(child->InlineOffsetToContainerBox() + paint_offset,
-                            child->Size());
-      current_backplate.Unite(box_rect);
+        PhysicalRect box_rect(child_item->Offset() + paint_offset,
+                              child_item->Size());
+        backplates.AddTextRect(box_rect);
       }
+      continue;
+    }
+    NOTREACHED();
   }
 
-  if (!current_backplate.IsEmpty())
-    paragraph_backplates.push_back(current_backplate);
-  return paragraph_backplates;
+  if (!backplates.current_backplate.IsEmpty())
+    backplates.paragraph_backplates.push_back(backplates.current_backplate);
+  return backplates.paragraph_backplates;
 }
 
 }  // anonymous namespace