DCHECK and TODO for crbug.com/786475 (Fieldset should not scroll)

This makes the failure more explicit, and make the expectation aligned
in pre-CompositeAfterPaint and CompositeAfterPaint for
external/wpt/html/rendering/non-replaced-elements/the-fieldset-and-legend-elements/fieldset-overflow.html.

Previously in CompositeAfterPaint the test triggered a DCHECK that was
not obvious of the reason.

Bug: 786475
Change-Id: I93c7df7c731b9f87d88d5ad509d2c6a4d4b10755
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2220159
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773249}

third_party/blink/renderer/core/paint/fieldset_painter.cc

@@ -44,6 +44,8 @@ void FieldsetPainter::PaintBoxDecorationBackground(
   }
 
   BoxDecorationData box_decoration_data(paint_info, layout_fieldset_);
+  // TODO(crbug.com/786475): Fieldset should not scroll.
+  DCHECK(!box_decoration_data.IsPaintingScrollingBackground());
   if (box_decoration_data.ShouldPaint() &&
       !DrawingRecorder::UseCachedDrawingIfPossible(
           paint_info.context, layout_fieldset_, paint_info.phase)) {

third_party/blink/renderer/core/paint/ng/ng_fieldset_painter.cc

@@ -42,6 +42,8 @@ void NGFieldsetPainter::PaintFieldsetDecorationBackground(
   PhysicalRect paint_rect(paint_offset, fieldset_size);
   const auto& fragment = fieldset_;
   BoxDecorationData box_decoration_data(paint_info, fragment);
+  // TODO(crbug.com/786475): Fieldset should not scroll.
+  DCHECK(!box_decoration_data.IsPaintingScrollingBackground());
   if (!box_decoration_data.ShouldPaint())
     return;
 

third_party/blink/web_tests/FlagExpectations/composite-after-paint

@@ -95,5 +95,4 @@ compositing/gestures/gesture-tapHighlight-composited-img.html [ Pass Failure ]
 http/tests/images/image-decode-in-frame.html [ Pass Failure ]
 
 # Failures after crrev.com/c/2212813
-external/wpt/html/rendering/non-replaced-elements/the-fieldset-and-legend-elements/fieldset-overflow.html [ Crash ]
 fast/table/cell-percent-padding.html [ Crash ]

third_party/blink/web_tests/TestExpectations

@@ -735,6 +735,8 @@ crbug.com/1068947 [ Win10 ] external/wpt/css/css-text-decor/text-underline-posit
 # Tentative mansonry tests
 crbug.com/1076027 external/wpt/css/css-grid/masonry.tentative/* [ Skip ]
 
+crbug.com/786475 external/wpt/html/rendering/non-replaced-elements/the-fieldset-and-legend-elements/fieldset-overflow.html [ Failure Crash ]
+
 # ====== Layout team owned tests to here ======
 
 # ====== LayoutNG-only failures from here ======
@@ -3197,7 +3199,6 @@ crbug.com/432153 external/wpt/css/css-masking/mask-image/mask-image-url-local-ma
 crbug.com/432153 external/wpt/css/css-masking/mask-image/mask-image-url-image.html [ Failure ]
 crbug.com/432153 external/wpt/css/css-masking/mask-image/mask-image-url-remote-mask.html [ Failure ]
 crbug.com/432153 external/wpt/css/css-masking/mask-image/mask-image-url-image-hash.html [ Failure ]
-crbug.com/626703 external/wpt/html/rendering/non-replaced-elements/the-fieldset-and-legend-elements/fieldset-overflow.html [ Failure ]
 crbug.com/626703 external/wpt/css/CSS2/floats/float-nowrap-9.html [ Failure ]
 crbug.com/626703 external/wpt/css/CSS2/floats/float-nowrap-8.html [ Failure ]
 crbug.com/626703 external/wpt/css/CSS2/floats/float-nowrap-7.html [ Failure ]