Rebaseline accessibility test for disable-layout-ng.

Missing part of
https://chromium-review.googlesource.com/c/chromium/src/+/2538266

I wish that linux_layout_tests_layout_ng_disabled were triggered a bit
more often, but since it isn't, things like this are bound to happen.

TBR=atotic@chromium.org

Bug: 958381
Change-Id: I0570151bf2081d4b0e14d42036e340f3ab2e5af0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2549945Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829219}

third_party/blink/web_tests/flag-specific/disable-layout-ng/accessibility/element-role-mapping-normal-expected.txt

@@ -172,13 +172,14 @@ element
         AXRole: AXCaption
             AXRole: AXStaticText "Caption"
                 AXRole: AXInlineTextBox "Caption"
-        AXRole: AXRow
-            AXRole: AXCell "Cell1"
-                AXRole: AXStaticText "Cell1"
-                    AXRole: AXInlineTextBox "Cell1"
-            AXRole: AXCell "Cell2"
-                AXRole: AXStaticText "Cell2"
-                    AXRole: AXInlineTextBox "Cell2"
+        AXRole: AXRowGroup
+            AXRole: AXRow
+                AXRole: AXCell "Cell1"
+                    AXRole: AXStaticText "Cell1"
+                        AXRole: AXInlineTextBox "Cell1"
+                AXRole: AXCell "Cell2"
+                    AXRole: AXStaticText "Cell2"
+                        AXRole: AXInlineTextBox "Cell2"
     AXRole: AXFigure "Fig1. - Blue Box"
         AXRole: AXImage "blue"
         AXRole: AXFigcaption