Handle incoming failing fieldset + block_frag test.

Fieldset elements require legacy layout, which also disables NG block
fragmentation. The test uses fieldset elements, while the ref doesn't.
There's a subtle rendering difference between the engines here. Not sure
if it's a bug or not, but we'll get to that once LayoutNGFieldset has
shipped.

TBR=futhark@chromium.org

Bug: 1028595
Change-Id: Ia63a2382719f02f8c24b485933a9fa1b56ee671e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1941310Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719935}

third_party/blink/web_tests/TestExpectations

@@ -862,6 +862,7 @@ crbug.com/797591 virtual/layout_ng_block_frag/fast/multicol/newmulticol/regular-
 
 ### With LayoutNGBlockFragmentation enabled:
 crbug.com/829028 virtual/layout_ng_block_frag/external/wpt/css/css-break/block-end-aligned-abspos-with-overflow.html [ Failure ]
+crbug.com/1028595 virtual/layout_ng_block_frag/external/wpt/css/css-break/fieldset-001.html [ Failure ]
 crbug.com/829028 virtual/layout_ng_block_frag/external/wpt/css/css-break/floats-and-text-narrow-and-short-dynamic.html [ Failure ]
 crbug.com/829028 virtual/layout_ng_block_frag/external/wpt/css/css-break/line-after-unbreakable-float-after-padding.html [ Failure ]
 crbug.com/829028 virtual/layout_ng_block_frag/external/wpt/css/css-break/widows-orphans-001.html [ Failure ]
@@ -2736,9 +2737,6 @@ crbug.com/626703 [ Win ] external/wpt/svg/painting/marker-orient-001.svg [ Failu
 crbug.com/626703 [ Linux ] external/wpt/infrastructure/reftest/reftest_wait_TestRendered.html [ Timeout ]
 crbug.com/626703 [ Mac ] external/wpt/infrastructure/reftest/reftest_wait_TestRendered.html [ Timeout ]
 crbug.com/626703 [ Win ] external/wpt/infrastructure/reftest/reftest_wait_TestRendered.html [ Timeout ]
-crbug.com/626703 [ Linux ] virtual/layout_ng_block_frag/external/wpt/css/css-break/fieldset-001.html [ Failure ]
-crbug.com/626703 [ Mac ] virtual/layout_ng_block_frag/external/wpt/css/css-break/fieldset-001.html [ Failure ]
-crbug.com/626703 [ Win ] virtual/layout_ng_block_frag/external/wpt/css/css-break/fieldset-001.html [ Failure ]
 crbug.com/626703 [ Linux ] external/wpt/mathml/presentation-markup/tokens/ms-001.html [ Failure ]
 crbug.com/626703 [ Mac ] external/wpt/mathml/presentation-markup/tokens/ms-001.html [ Failure ]
 crbug.com/626703 [ Win ] external/wpt/mathml/presentation-markup/tokens/ms-001.html [ Failure ]