[LayoutNG] Fieldset borders with legend

Extend the fix in CL:2551748 to include the legend.

Bug: 1150803
Change-Id: Ic4a5879baf6da2a7f8a8953508674e0992dbb7f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2572122
Commit-Queue: Alison Maher <almaher@microsoft.com>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834812}

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

@@ -105,7 +105,7 @@ void NGFieldsetPainter::PaintBoxDecorationBackground(
           box_decoration_data.GetBackgroundBleedAvoidance())) {
     state_saver.Save();
     FloatRoundedRect border = RoundedBorderGeometry::PixelSnappedRoundedBorder(
-        style, paint_rect, fieldset_.SidesToInclude());
+        style, contracted_rect, fieldset_.SidesToInclude());
     graphics_context.ClipRoundedRect(border);
 
     if (box_decoration_data.GetBackgroundBleedAvoidance() ==

third_party/blink/web_tests/external/wpt/html/rendering/non-replaced-elements/the-fieldset-and-legend-elements/fieldset-border-radius-with-alpha-ref.html

@@ -2,10 +2,10 @@
 <style>
 div {
     background-color: green;
-    height: 150px;
+    height: 110px;
     position: absolute;
     width: 150px;
-    top: 50px;
+    top: 70px;
 }
 </style>
 <p>There should be no red.</p>

third_party/blink/web_tests/external/wpt/html/rendering/non-replaced-elements/the-fieldset-and-legend-elements/fieldset-border-radius-with-alpha.html

@@ -9,14 +9,18 @@ fieldset {
     height: 100px;
     width: 100px;
 }
+legend {
+    height: 50px;
+    width: 50px;
+}
 div {
     background-color: green;
-    height: 150px;
+    height: 110px;
     position: absolute;
     width: 150px;
-    top: 50px;
+    top: 70px;
 }
 </style>
 <p>There should be no red.</p>
-<fieldset></fieldset>
+<fieldset><legend></legend></fieldset>
 <div></div>