css-flexbox: Fix static position for out-of-flow webkit-box

Ian was of the opinion the horizontal version should be the
same as the vertical position.

BUG=993813

Change-Id: I6238b5fdff67701335e778d2dca6fd5b40c0ea9c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1826871Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700458}

third_party/blink/renderer/core/layout/layout_flexible_box.cc

@@ -1294,7 +1294,7 @@ LayoutUnit LayoutFlexibleBox::StaticCrossAxisPositionForPositionedChild(
 LayoutUnit LayoutFlexibleBox::StaticInlinePositionForPositionedChild(
     const LayoutBox& child) {
   const LayoutUnit start_offset = StartOffsetForContent();
-  if (IsColumnFlow() && StyleRef().IsDeprecatedWebkitBox())
+  if (StyleRef().IsDeprecatedWebkitBox())
     return start_offset;
   return start_offset + (IsColumnFlow()
                              ? StaticCrossAxisPositionForPositionedChild(child)