[LayoutNG] Forced breaks trump break avoidance.

Even when there's a forced break deep inside a break-inside:avoid
subtree, we should allow the break.

https://www.w3.org/TR/css-break-3/#breaking-controls

Bug: 829028
Change-Id: I2e098113d3bd73b506cffa22aa87c90e1f7186e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1829348
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701476}

third_party/blink/renderer/core/layout/ng/ng_block_layout_algorithm.cc

@@ -2022,8 +2022,9 @@ bool NGBlockLayoutAlgorithm::BreakBeforeChildIfNeeded(
           DynamicTo<NGBlockBreakToken>(physical_fragment.BreakToken())) {
     // The block child broke inside. We now need to decide whether to keep that
     // break, or if it would be better to break before it.
-    if (!child_token->HasLastResortBreak() &&
-        !IsAvoidBreakValue(ConstraintSpace(), child.Style().BreakInside())) {
+    if ((!child_token->HasLastResortBreak() &&
+         !IsAvoidBreakValue(ConstraintSpace(), child.Style().BreakInside())) ||
+        layout_result.HasForcedBreak()) {
       // The break inside is perfect. Keep it.
       return false;
     }

third_party/blink/web_tests/TestExpectations

@@ -1805,7 +1805,6 @@ crbug.com/591099 virtual/layout_ng_experimental/fragmentation/auto-scrollbar-shr
 crbug.com/591099 virtual/layout_ng_experimental/fragmentation/become-unfragmented-with-lines.html [ Crash Pass ]
 crbug.com/591099 virtual/layout_ng_experimental/fragmentation/become-unfragmented-with-unbreakable-blocks.html [ Crash Pass ]
 crbug.com/591099 virtual/layout_ng_experimental/fragmentation/block-after-float-first-child.html [ Failure ]
-crbug.com/591099 virtual/layout_ng_experimental/fragmentation/break-inside-avoid-with-forced-break.html [ Failure ]
 crbug.com/591099 virtual/layout_ng_experimental/fragmentation/change-fragmentainer-height-block-float-2.html [ Failure ]
 crbug.com/591099 virtual/layout_ng_experimental/fragmentation/change-fragmentainer-height-block-float.html [ Failure ]
 crbug.com/591099 virtual/layout_ng_experimental/fragmentation/change-fragmentainer-height-inline-float.html [ Failure ]