RubyNG: Make ScrollableOverflow compatible with the legacy layout

Before this CL ScrollableOverflow in LayoutNG was always larger than the
line's bounding box.  It was not compatible with the legacy layout, and
it's helpless for <rt> positioning.  This CL makes ScrollableOveflow
compatible with the legacy layout.

Bug: 1069817
Change-Id: I876874966088a59fdc218a83342c1d0e4c68ee87
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225685
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774069}

third_party/blink/renderer/core/layout/ng/inline/ng_physical_line_box_fragment.cc

@@ -71,15 +71,21 @@ NGLineHeightMetrics NGPhysicalLineBoxFragment::BaselineMetrics() const {
 namespace {
 
 // Include the inline-size of the line-box in the overflow.
+// Do not update block offset and block size of |overflow|.
 inline void AddInlineSizeToOverflow(const PhysicalRect& rect,
                                     const WritingMode container_writing_mode,
                                     PhysicalRect* overflow) {
   PhysicalRect inline_rect;
   inline_rect.offset = rect.offset;
-  if (IsHorizontalWritingMode(container_writing_mode))
+  if (IsHorizontalWritingMode(container_writing_mode)) {
     inline_rect.size.width = rect.size.width;
-  else
+    inline_rect.offset.top = overflow->offset.top;
+    inline_rect.size.height = overflow->size.height;
+  } else {
     inline_rect.size.height = rect.size.height;
+    inline_rect.offset.left = overflow->offset.left;
+    inline_rect.size.width = overflow->size.width;
+  }
   overflow->UniteEvenIfEmpty(inline_rect);
 }