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

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NGConstraintSpace_h
 #define NGConstraintSpace_h
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_physical_constraint_space.h"
 #include "core/layout/ng/ng_writing_mode.h"
@@ skipping 67 matching lines @@
   NGLogicalSize ContainerSize() const;
 
   // Offset relative to the root constraint space.
   NGLogicalOffset Offset() const { return offset_; }
 
   // Returns the effective size of the constraint space. Equal to the
   // ContainerSize() for the root constraint space but derived constraint spaces
   // return the size of the layout opportunity.
   virtual NGLogicalSize Size() const { return size_; }
 
+  // Whether the current constraint space is for the newly established Block
+  // Formatting Context(BFC).
+  bool IsNewBfc() const { return is_new_bfc_; }

[ikilpatrick, 2016/09/29 00:18:11]

thought we were just going to have a method on NGBox with TODO to move to
ComputedStyle?

[Gleb Lanbin, 2016/09/29 17:11:15]

Acknowledged.

+
   // 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
   // constraint space modified to reserve space for a scrollbar.
   bool InlineTriggersScrollbar() const;
   bool BlockTriggersScrollbar() const;
 
   // Some layout modes “stretch” their children to a fixed size (e.g. flex,
   // grid). These flags represented whether a layout needs to produce a
   // fragment that satisfies a fixed constraint in the inline and block
@@ skipping 14 matching lines @@
       unsigned clear = NGClearNone,
       bool for_inline_or_bfc = false);
 
   DEFINE_INLINE_VIRTUAL_TRACE() { visitor->trace(physical_space_); }
 
   // The setters for the NGConstraintSpace should only be used when constructing
   // a derived NGConstraintSpace.
   void SetOverflowTriggersScrollbar(bool inlineTriggers, bool blockTriggers);
   void SetFixedSize(bool inlineFixed, bool blockFixed);
   void SetFragmentationType(NGFragmentationType);
+  void SetIsNewBfc(bool is_new_bfc) { is_new_bfc_ = is_new_bfc; }
 
   String ToString() const;
 
  private:
   Member<NGPhysicalConstraintSpace> physical_space_;
   NGLogicalOffset offset_;
   NGLogicalSize size_;
   unsigned writing_mode_ : 3;
   unsigned direction_ : 1;
+  // Whether the current constraint space is for the newly established Block
+  // Formatting Context(BFC).
+  bool is_new_bfc_ : 1;
 };
 
 inline std::ostream& operator<<(std::ostream& stream,
                                 const NGConstraintSpace& value) {
   return stream << value.ToString();
 }
 
 }  // namespace blink
 
 #endif  // NGConstraintSpace_h