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

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

Index: third_party/WebKit/Source/core/layout/ng/ng_box.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_box.cc b/third_party/WebKit/Source/core/layout/ng/ng_box.cc
index 3c9667beefb82b6b1d7eaa7eda8b6b979216f057..c5664492f8c7902d716e90967233c1b5a5c55ec8 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_box.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_box.cc
@@ -15,6 +15,14 @@
 #include "core/layout/ng/ng_writing_mode.h"
 
 namespace blink {
+namespace {
+// TODO(layout-ng): Add m_isNewFc flag to ComputedStyle and set it from
+// StyleResolver instead of getting it calculated by createsNewFormattingContext
+bool IsNewFormattingContext(const LayoutBox* layout_box) {
+  return layout_box && toLayoutBlock(layout_box)->createsNewFormattingContext();
+}
+}  // namespace
+
 NGBox::NGBox(LayoutObject* layout_object)
     : layout_box_(toLayoutBox(layout_object)) {
   DCHECK(layout_box_);
@@ -38,6 +46,8 @@ bool NGBox::Layout(const NGConstraintSpace* constraint_space,
     NGConstraintSpace* child_constraint_space = new NGConstraintSpace(
         FromPlatformWritingMode(Style()->getWritingMode()),
         FromPlatformDirection(Style()->direction()), constraint_space);
+    child_constraint_space->SetIsNewFormattingContext(
+        IsNewFormattingContext(layout_box_));
 
     NGPhysicalFragment* fragment = nullptr;
     if (!algorithm_->Layout(child_constraint_space, &fragment))