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

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

Index: third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc b/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
index cae190747cc9d0599fe6ae29d473a9dcced13a91..5784826ca95b110edb7bb130de8f3431b36a56a9 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
@@ -18,7 +18,8 @@ NGConstraintSpace::NGConstraintSpace(NGWritingMode writing_mode,
           container_size.ConvertToPhysical(writing_mode))),
       size_(container_size),
       writing_mode_(writing_mode),
-      direction_(direction) {}
+      direction_(direction),
+      is_root_(false) {}
 
 NGConstraintSpace::NGConstraintSpace(NGWritingMode writing_mode,
                                      NGDirection direction,
@@ -26,7 +27,8 @@ NGConstraintSpace::NGConstraintSpace(NGWritingMode writing_mode,
     : physical_space_(physical_space),
       size_(physical_space->ContainerSize().ConvertToLogical(writing_mode)),
       writing_mode_(writing_mode),
-      direction_(direction) {}
+      direction_(direction),
+      is_root_(false) {}
 
 NGConstraintSpace::NGConstraintSpace(NGWritingMode writing_mode,
                                      NGDirection direction,
@@ -35,7 +37,8 @@ NGConstraintSpace::NGConstraintSpace(NGWritingMode writing_mode,
       offset_(constraint_space->Offset()),
       size_(constraint_space->Size()),
       writing_mode_(writing_mode),
-      direction_(direction) {}
+      direction_(direction),
+      is_root_(constraint_space->IsRoot()) {}
 
 NGConstraintSpace::NGConstraintSpace(const NGConstraintSpace& other,
                                      NGLogicalOffset offset,
@@ -44,13 +47,17 @@ NGConstraintSpace::NGConstraintSpace(const NGConstraintSpace& other,
       offset_(offset),
       size_(size),
       writing_mode_(other.WritingMode()),
-      direction_(other.Direction()) {}
+      direction_(other.Direction()),
+      is_root_(false) {}
 
 NGConstraintSpace::NGConstraintSpace(NGWritingMode writing_mode,
                                      NGDirection direction,
                                      const NGConstraintSpace& other,
                                      NGLogicalSize size)
-    : size_(size), writing_mode_(writing_mode), direction_(direction) {
+    : size_(size),
+      writing_mode_(writing_mode),
+      direction_(direction),
+      is_root_(false) {
   physical_space_ =
       new NGPhysicalConstraintSpace(size.ConvertToPhysical(writing_mode));
   for (const NGExclusion& exclusion : other.PhysicalSpace()->Exclusions()) {
@@ -93,6 +100,7 @@ NGConstraintSpace* NGConstraintSpace::CreateFromLayoutObject(
       box.styleRef().overflowInlineDirection() == OverflowAuto,
       box.styleRef().overflowBlockDirection() == OverflowAuto);
   derived_constraint_space->SetFixedSize(fixed_inline, fixed_block);
+  derived_constraint_space->SetIsRoot();

[ikilpatrick, 2016/09/28 20:11:20]

Is this flag for only the root document element? or for the root of the block
formatting context?

   return derived_constraint_space;
 }