Compute margin block start for 1st block in LayoutNG root constraint space

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

Index: third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h b/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h
index 67bc21fa2adbaef016fcbaebcc1e4d8d042e7609..38f0ed20dc51aa5669e3e0f1fb637d17727d20d0 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h
+++ b/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.h
@@ -85,6 +85,10 @@ class CORE_EXPORT NGConstraintSpace final
   // return the size of the layout opportunity.
   virtual NGLogicalSize Size() const { return size_; }
 
+  // Whether the current constraint space is for the LayoutNG

[mstensho (USE GERRIT), 2016/09/28 11:49:33]

Shouldn't it rather just say "the document root element's children", or
something like that? As far I understand, this is merely a spec thing (shouldn't
collapse margins with those of the root element), and not something
LayoutNG-specific?

[Gleb Lanbin, 2016/09/28 17:26:07]

Done.

+  // root element's children.
+  bool IsRoot() const { return is_root; }
+
   // Whether exceeding the containerSize triggers the presence of a scrollbar
   // for the indicated direction.
   // If exceeded the current layout should be aborted and invoked again with a
@@ -119,6 +123,7 @@ class CORE_EXPORT NGConstraintSpace final
   void SetOverflowTriggersScrollbar(bool inlineTriggers, bool blockTriggers);
   void SetFixedSize(bool inlineFixed, bool blockFixed);
   void SetFragmentationType(NGFragmentationType);
+  void SetIsRoot() { is_root = true; }
 
   String ToString() const;
 
@@ -128,6 +133,9 @@ class CORE_EXPORT NGConstraintSpace final
   NGLogicalSize size_;
   unsigned writing_mode_ : 3;
   unsigned direction_ : 1;
+  // Whether the current constraint space is for the LayoutNG
+  // root element's children.
+  bool is_root : 1;

[mstensho (USE GERRIT), 2016/09/28 11:49:33]

Missing trailing underscore.

[Gleb Lanbin, 2016/09/28 17:26:07]

Done.

 };
 
 inline std::ostream& operator<<(std::ostream& stream,