[LayoutNG] Add floats_bfc_offset to 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/geometry/ng_logical_offset.h"
 #include "core/layout/ng/geometry/ng_logical_size.h"
@@ skipping 76 matching lines @@
   }
 
   bool IsBlockDirectionTriggersScrollbar() const {
     return is_block_direction_triggers_scrollbar_;
   }
 
   // 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
   // direction respectively.
+  //
   // If these flags are true, the AvailableSize() is interpreted as the fixed
   // border-box size of this box in the respective dimension.
   bool IsFixedSizeInline() const { return is_fixed_size_inline_; }
 
   bool IsFixedSizeBlock() const { return is_fixed_size_block_; }
 
   // Whether an auto inline-size should be interpreted as shrink-to-fit
   // (ie. fit-content). This is used for inline-block, floats, etc.
   bool IsShrinkToFit() const { return is_shrink_to_fit_; }
 
   // If specified a layout should produce a Fragment which fragments at the
   // blockSize if possible.
   NGFragmentationType BlockFragmentationType() const;
 
   // Return true if this contraint space participates in a fragmentation
   // context.
   bool HasBlockFragmentation() const {
     return BlockFragmentationType() != kFragmentNone;
   }
 
   NGMarginStrut MarginStrut() const { return margin_strut_; }
 
+  // The BfcOffset is where the MarginStrut is placed within the block
+  // formatting context.
+  //
+  // The current layout or a descendant layout may "resolve" the BFC offset,
+  // i.e. decide where the current fragment should be placed within the BFC.
+  //
+  // This is done by:
+  //   bfc_block_offset =
+  //     space.BfcOffset().block_offset + space.MarginStrut().Sum();
+  //
+  // The BFC offset can get "resolved" in many circumstances (including, but
+  // not limited to):
+  //   - block_start border or padding in the current layout.
+  //   - Text content, atomic inlines, (see NGLineBreaker).
+  //   - The current layout having a block_size.
   NGLogicalOffset BfcOffset() const { return bfc_offset_; }
 
+  // If present, and the current layout hasn't resolved its BFC offset yet (see
+  // BfcOffset), the layout should position all of its unpositioned floats at
+  // this offset.
+  //
+  // This value should be propogated to child layouts if the current layout
+  // hasn't resolved its BFC offset yet.
+  //
+  // This value is calculated *after* an initial pass of the tree, this value
+  // should only be present during the second pass.
+  WTF::Optional<NGLogicalOffset> FloatsBfcOffset() const {
+    return floats_bfc_offset_;
+  }
+
   Vector<RefPtr<NGUnpositionedFloat>>& UnpositionedFloats() {
     return unpositioned_floats_;
   }
 
   WTF::Optional<LayoutUnit> ClearanceOffset() const {
     return clearance_offset_;
   }
 
   bool operator==(const NGConstraintSpace&) const;
   bool operator!=(const NGConstraintSpace&) const;
@@ skipping 12 matching lines @@
                     bool is_fixed_size_inline,
                     bool is_fixed_size_block,
                     bool is_shrink_to_fit,
                     bool is_inline_direction_triggers_scrollbar,
                     bool is_block_direction_triggers_scrollbar,
                     NGFragmentationType block_direction_fragmentation_type,
                     bool is_new_fc,
                     bool is_anonymous,
                     const NGMarginStrut& margin_strut,
                     const NGLogicalOffset& bfc_offset,
+                    const WTF::Optional<NGLogicalOffset>& floats_bfc_offset,
                     const std::shared_ptr<NGExclusions>& exclusions,
                     Vector<RefPtr<NGUnpositionedFloat>>& unpositioned_floats,
                     const WTF::Optional<LayoutUnit>& clearance_offset);
 
   NGPhysicalSize InitialContainingBlockSize() const {
     return initial_containing_block_size_;
   }
 
   NGLogicalSize available_size_;
   NGLogicalSize percentage_resolution_size_;
@@ skipping 15 matching lines @@
   // formatting Context
   unsigned is_new_fc_ : 1;
 
   unsigned is_anonymous_ : 1;
 
   unsigned writing_mode_ : 3;
   unsigned direction_ : 1;
 
   NGMarginStrut margin_strut_;
   NGLogicalOffset bfc_offset_;
+  WTF::Optional<NGLogicalOffset> floats_bfc_offset_;
+
   const std::shared_ptr<NGExclusions> exclusions_;
   WTF::Optional<LayoutUnit> clearance_offset_;
   Vector<RefPtr<NGUnpositionedFloat>> unpositioned_floats_;
 };
 
 inline std::ostream& operator<<(std::ostream& stream,
                                 const NGConstraintSpace& value) {
   return stream << value.ToString();
 }
 
 }  // namespace blink
 
 #endif  // NGConstraintSpace_h