[LayoutNG] Allow block-flow layout to be fragmented using new approach.

third_party/WebKit/Source/core/layout/ng/ng_fragment_builder.h

Index: third_party/WebKit/Source/core/layout/ng/ng_fragment_builder.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_fragment_builder.h b/third_party/WebKit/Source/core/layout/ng/ng_fragment_builder.h
index 7e9338c0661019446a9730c120e9c23869808a54..3a82c44d014f0d6b6f2fc774586c3b93dbe407a0 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_fragment_builder.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_fragment_builder.h
@@ -35,6 +35,7 @@ class CORE_EXPORT NGFragmentBuilder final {
   NGFragmentBuilder& AddChild(RefPtr<NGLayoutResult>, const NGLogicalOffset&);
   NGFragmentBuilder& AddChild(RefPtr<NGPhysicalFragment>,
                               const NGLogicalOffset&);
+
   NGFragmentBuilder& AddFloatingObject(NGFloatingObject*,
                                        const NGLogicalOffset&);
 
@@ -75,11 +76,15 @@ class CORE_EXPORT NGFragmentBuilder final {
   NGFragmentBuilder& AddOutOfFlowDescendant(NGBlockNode*,
                                             const NGStaticPosition&);
 
-  void SetBreakToken(NGBreakToken* token) {
-    DCHECK(!break_token_);
-    break_token_ = token;
+  // Sets how much of the block size we've used so far for this box.
+  //
+  // This will result in a fragment which has an unfinished break token, which
+  // contains this information.
+  NGFragmentBuilder& SetUsedBlockSize(LayoutUnit used_block_size) {
+    used_block_size_ = used_block_size;
+    did_break_ = true;
+    return *this;
   }
-  bool HasBreakToken() const { return break_token_; }
 
   NGFragmentBuilder& SetEndMarginStrut(const NGMarginStrut& from) {
     end_margin_strut_ = from;
@@ -109,6 +114,8 @@ class CORE_EXPORT NGFragmentBuilder final {
     return bfc_offset_;
   }
 
+  bool DidBreak() const { return did_break_; }
+
  private:
   // Out-of-flow descendant placement information.
   // The generated fragment must compute NGStaticPosition for all
@@ -140,6 +147,11 @@ class CORE_EXPORT NGFragmentBuilder final {
   Vector<RefPtr<NGPhysicalFragment>> children_;
   Vector<NGLogicalOffset> offsets_;
 
+  bool did_break_;
+  LayoutUnit used_block_size_;
+
+  Persistent<HeapVector<Member<NGBreakToken>>> child_break_tokens_;
+
   WeakBoxList out_of_flow_descendant_candidates_;
   Vector<OutOfFlowPlacement> out_of_flow_candidate_placements_;
 
@@ -153,8 +165,6 @@ class CORE_EXPORT NGFragmentBuilder final {
   Vector<NGLogicalOffset> floating_object_offsets_;
   Vector<Persistent<NGFloatingObject>> positioned_floats_;
 
-  Persistent<NGBreakToken> break_token_;
-
   WTF::Optional<NGLogicalOffset> bfc_offset_;
   NGMarginStrut end_margin_strut_;
 };