[LayoutNG] Fix coordinates for items in column flexboxes

They need to be transposed from what the underlying flex algorithm
generates.

Bug: 845235
Change-Id: Ib967035798a148bce0e853656598bba366d45b70
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1749668
Commit-Queue: David Grogan <dgrogan@chromium.org>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686239}

third_party/blink/renderer/core/layout/flexible_box_algorithm.h

@@ -138,6 +138,7 @@ class FlexItem {
 
   // When set by the caller, this should be the size pre-stretching.
   LayoutUnit cross_axis_size;
+  // The algorithm stores the main axis offset in X and cross axis offset in Y.
   LayoutPoint desired_location;
 
   bool frozen;

third_party/blink/renderer/core/layout/ng/ng_flex_layout_algorithm.cc

@@ -495,13 +495,15 @@ void NGFlexLayoutAlgorithm::GiveLinesAndItemsFinalPositionAndSize() {
       // TODO(dgrogan): Add an extra pass for kColumnReverse containers like
       // legacy does in LayoutColumnReverse.
 
-      // AddChild treats location parameter as logical offset from parent rect.
-      // TODO(dgrogan): Does this need to transpose the location for
-      // non-horizontal flexboxes, like
-      // LayoutFlexibleBox::SetFlowAwareLocationForChild does?
-      container_builder_.AddChild(
-          flex_item.layout_result->PhysicalFragment(),
-          {flex_item.desired_location.X(), flex_item.desired_location.Y()});
+      // flex_item.desired_location stores the main axis offset in X and the
+      // cross axis offset in Y. But AddChild wants offset from parent
+      // rectangle, so we have to transpose for columns. AddChild takes care of
+      // any writing mode differences though.
+      LayoutPoint location = is_column_
+                                 ? flex_item.desired_location.TransposedPoint()
+                                 : flex_item.desired_location;
+      container_builder_.AddChild(flex_item.layout_result->PhysicalFragment(),
+                                  {location.X(), location.Y()});
     }
   }
 }