[LayoutNG] Untangle block-offset relativeness for BreakBeforeChildIfNeeded().

BreakBeforeChildIfNeeded() needs to make the block-offset relative to
the fragmentainer, so passing an offset that's relative to the BFC gives
less work than passing one relative to the containing block.

This is just cleanup - no behavior changes.

Change-Id: I49fa3415e37191e285c2d4844465862d46ebc58f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2023887Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735756}

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

@@ -1231,13 +1231,6 @@ NGLayoutResult::EStatus NGBlockLayoutAlgorithm::HandleNewFormattingContext(
         /* abort_if_cleared */ false, &child_bfc_offset);
   }
 
-  const auto& physical_fragment = layout_result->PhysicalFragment();
-  NGFragment fragment(ConstraintSpace().GetWritingMode(), physical_fragment);
-
-  LogicalOffset logical_offset = LogicalFromBfcOffsets(
-      child_bfc_offset, ContainerBfcOffset(), fragment.InlineSize(),
-      container_builder_.Size().inline_size, ConstraintSpace().Direction());
-
   if (ConstraintSpace().HasBlockFragmentation()) {
     bool has_container_separation =
         has_processed_first_child_ || child_margin_got_separated ||
@@ -1245,7 +1238,7 @@ NGLayoutResult::EStatus NGBlockLayoutAlgorithm::HandleNewFormattingContext(
         layout_result->IsPushedByFloats();
     NGBreakStatus break_status = BreakBeforeChildIfNeeded(
         child, *layout_result, previous_inflow_position,
-        logical_offset.block_offset, has_container_separation);
+        child_bfc_offset.block_offset, has_container_separation);
     if (break_status == NGBreakStatus::kBrokeBefore)
       return NGLayoutResult::kSuccess;
     if (break_status == NGBreakStatus::kNeedsEarlierBreak)
@@ -1255,6 +1248,13 @@ NGLayoutResult::EStatus NGBlockLayoutAlgorithm::HandleNewFormattingContext(
     container_builder_.SetPreviousBreakAfter(break_after);
   }
 
+  const auto& physical_fragment = layout_result->PhysicalFragment();
+  NGFragment fragment(ConstraintSpace().GetWritingMode(), physical_fragment);
+
+  LogicalOffset logical_offset = LogicalFromBfcOffsets(
+      child_bfc_offset, ContainerBfcOffset(), fragment.InlineSize(),
+      container_builder_.Size().inline_size, ConstraintSpace().Direction());
+
   if (!PositionOrPropagateListMarker(*layout_result, &logical_offset,
                                      previous_inflow_position))
     return NGLayoutResult::kBfcBlockOffsetResolved;
@@ -1732,7 +1732,8 @@ NGLayoutResult::EStatus NGBlockLayoutAlgorithm::FinishInflow(
   LogicalOffset logical_offset = CalculateLogicalOffset(
       fragment, layout_result->BfcLineOffset(), child_bfc_block_offset);
 
-  if (ConstraintSpace().HasBlockFragmentation()) {
+  if (ConstraintSpace().HasBlockFragmentation() &&
+      container_builder_.BfcBlockOffset() && child_bfc_block_offset) {
     // Floats only cause container separation for the outermost block child that
     // gets pushed down (the container and the child may have adjoining
     // block-start margins).
@@ -1741,7 +1742,7 @@ NGLayoutResult::EStatus NGBlockLayoutAlgorithm::FinishInflow(
                                        !container_builder_.IsPushedByFloats());
     NGBreakStatus break_status = BreakBeforeChildIfNeeded(
         child, *layout_result, previous_inflow_position,
-        logical_offset.block_offset, has_container_separation);
+        *child_bfc_block_offset, has_container_separation);
     if (break_status == NGBreakStatus::kBrokeBefore)
       return NGLayoutResult::kSuccess;
     if (break_status == NGBreakStatus::kNeedsEarlierBreak)
@@ -2080,14 +2081,13 @@ NGBreakStatus NGBlockLayoutAlgorithm::BreakBeforeChildIfNeeded(
     NGLayoutInputNode child,
     const NGLayoutResult& layout_result,
     NGPreviousInflowPosition* previous_inflow_position,
-    LayoutUnit block_offset,
+    LayoutUnit bfc_block_offset,
     bool has_container_separation) {
   DCHECK(ConstraintSpace().HasBlockFragmentation());
 
   // If the BFC offset is unknown, there's nowhere to break, since there's no
   // non-empty child content yet (as that would have resolved the BFC offset).
-  if (!container_builder_.BfcBlockOffset())
-    return NGBreakStatus::kContinue;
+  DCHECK(container_builder_.BfcBlockOffset());
 
   // If we already know where to insert the break, we already know that it's not
   // going to be here, since that's something we check before entering layout of
@@ -2096,8 +2096,7 @@ NGBreakStatus NGBlockLayoutAlgorithm::BreakBeforeChildIfNeeded(
     return NGBreakStatus::kContinue;
 
   LayoutUnit fragmentainer_block_offset =
-      ConstraintSpace().FragmentainerOffsetAtBfc() +
-      *container_builder_.BfcBlockOffset() + block_offset;
+      ConstraintSpace().FragmentainerOffsetAtBfc() + bfc_block_offset;
 
   if (has_container_separation) {
     EBreakBetween break_between =

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

@@ -232,7 +232,7 @@ class CORE_EXPORT NGBlockLayoutAlgorithm
   NGBreakStatus BreakBeforeChildIfNeeded(NGLayoutInputNode child,
                                          const NGLayoutResult&,
                                          NGPreviousInflowPosition*,
-                                         LayoutUnit block_offset,
+                                         LayoutUnit bfc_block_offset,
                                          bool has_container_separation);
 
   // Look for a better breakpoint (than we already have) between lines (i.e. a