[LayoutNG] Cleanup how NGBlockNode sets/clears cached resluts and paint fragments

This patch cleans up how NGBlockNode sets/clears cached
results and paint fragments, reducing an "if" and avoiding
to clear paint fragment if we're going to update.

No behavior changes.

Bug: 714962
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I462a8d1632cb2bd6b2cef2fa4cb71493a97b4160
Reviewed-on: https://chromium-review.googlesource.com/1175749Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586655}

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

@@ -233,35 +233,31 @@ void NGBlockNode::FinishLayout(const NGConstraintSpace& constraint_space,
   if (!IsBlockLayoutComplete(constraint_space, *layout_result))
     return;
 
-  // TODO(kojii): Even when we paint fragments, there seem to be some data we
-  // need to copy to LayoutBox. Review if we can minimize the copy.
-  LayoutBlockFlow* block_flow =
-      box_->IsLayoutNGMixin() ? ToLayoutBlockFlow(box_) : nullptr;
-  if (block_flow) {
+  DCHECK(layout_result->PhysicalFragment());
+
+  if (box_->IsLayoutNGMixin()) {
+    LayoutBlockFlow* block_flow = ToLayoutBlockFlow(box_);
     block_flow->SetCachedLayoutResult(constraint_space, break_token,
                                       layout_result);
-    if (layout_result->Status() == NGLayoutResult::kSuccess &&
-        !constraint_space.IsIntermediateLayout())
-      block_flow->SetPaintFragment(break_token, nullptr);
-  }
 
-  DCHECK(layout_result->PhysicalFragment());
-
-  NGLayoutInputNode first_child = FirstChild();
-  if (block_flow && first_child && first_child.IsInline()) {
-    NGBoxStrut scrollbars = GetScrollbarSizes();
-    CopyFragmentDataToLayoutBoxForInlineChildren(
-        ToNGPhysicalBoxFragment(*layout_result->PhysicalFragment()),
-        layout_result->PhysicalFragment()->Size().width -
-            scrollbars.block_start,
-        Style().IsFlippedBlocksWritingMode());
-
-    block_flow->SetPaintFragment(break_token,
-                                 layout_result->PhysicalFragment());
+    NGLayoutInputNode first_child = FirstChild();
+    if (first_child && first_child.IsInline()) {
+      NGBoxStrut scrollbars = GetScrollbarSizes();
+      CopyFragmentDataToLayoutBoxForInlineChildren(
+          ToNGPhysicalBoxFragment(*layout_result->PhysicalFragment()),
+          layout_result->PhysicalFragment()->Size().width -
+              scrollbars.block_start,
+          Style().IsFlippedBlocksWritingMode());
+
+      block_flow->SetPaintFragment(break_token,
+                                   layout_result->PhysicalFragment());
+    } else {
+      // We still need to clear paint fragments in case it had inline children,
+      // and thus had NGPaintFragment.
+      block_flow->SetPaintFragment(break_token, nullptr);
+    }
   }
 
-  // TODO(kojii): Even when we paint fragments, there seem to be some data we
-  // need to copy to LayoutBox. Review if we can minimize the copy.
   CopyFragmentDataToLayoutBox(constraint_space, *layout_result);
 }