Ignore zero-height fragments during margin collapsing

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 998a2aa8fe1e10f6d3164c892b70c839608de132..f9078a310c223a415f89e7aba05a9a5bf40e410b 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
@@ -26,11 +26,12 @@ class CORE_EXPORT NGFragmentBuilder final
 
   NGFragmentBuilder& AddChild(NGFragment*, NGLogicalOffset);
 
-  // Sets MarginStrut for the resultant fragment.
-  // These 2 methods below should be only called once as we update the
-  // fragment's MarginStrut block start/end from first/last children MarginStrut
-  NGFragmentBuilder& SetMarginStrutBlockStart(const NGMarginStrut& from);
-  NGFragmentBuilder& SetMarginStrutBlockEnd(const NGMarginStrut& from);
+  // Updates block-{start|end} of the currently constructed fragment.
+  //
+  // This method is supposed to be called on every child but it only updates
+  // the block-start once (on the first non-zero height child fragment) and
+  // keeps updating block-end (on every non-zero height child).
+  NGFragmentBuilder& UpdateMarginStrut(const NGMarginStrut& from);
 
   // Offsets are not supposed to be set during fragment construction, so we
   // do not provide a setter here.
@@ -41,6 +42,9 @@ class CORE_EXPORT NGFragmentBuilder final
   DEFINE_INLINE_VIRTUAL_TRACE() { visitor->trace(children_); }
 
  private:
+  void SetMarginStrutBlockStart(const NGMarginStrut& from);
+  void SetMarginStrutBlockEnd(const NGMarginStrut& from);
+
   NGPhysicalFragmentBase::NGFragmentType type_;
   NGWritingMode writing_mode_;
   NGDirection direction_;
@@ -53,10 +57,8 @@ class CORE_EXPORT NGFragmentBuilder final
   HeapVector<Member<NGPhysicalFragmentBase>> children_;
   Vector<NGLogicalOffset> offsets_;
 
-  // Whether MarginStrut block start/end was updated.
-  // It's used for DCHECK safety check.
+  // Whether MarginStrut block start is updated.
   bool is_margin_strut_block_start_updated_ : 1;
-  bool is_margin_strut_block_end_updated_ : 1;
 };
 
 }  // namespace blink