Bugfix in check elimination with a regression test.

src/hydrogen-check-elimination.cc

Index: src/hydrogen-check-elimination.cc
diff --git a/src/hydrogen-check-elimination.cc b/src/hydrogen-check-elimination.cc
index f15267349f2e09af355ad0c900b5814e79095165..6e6a84cc7b3485d64d5813a9288bd58ea7f7e22d 100644
--- a/src/hydrogen-check-elimination.cc
+++ b/src/hydrogen-check-elimination.cc
@@ -338,7 +338,9 @@ class HCheckTable : public ZoneObject {
             HCheckMaps* check = HCheckMaps::cast(entry->check_);
             TRACE(("CheckMaps #%d at B%d narrowed\n", check->id(),
                 check->block()->block_id()));
+            // Update map set and ensure that the check is alive.
             check->set_map_set(intersection, graph->zone());
+            check->ClearFlag(HValue::kIsDead);
             TRACE(("Replacing redundant CheckMaps #%d at B%d with #%d\n",
                 instr->id(), instr->block()->block_id(), entry->check_->id()));
             instr->DeleteAndReplaceWith(entry->check_);