[heap] Fix debug check in ShrinkToHighWaterMark

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index e95f87d23d02585452d472c6eb09e3b082b0a921..8710a5f54b00057d0a093c210200aea2f7bac1a0 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -795,6 +795,12 @@ size_t Page::ShrinkToHighWaterMark() {
   }
   if (filler2 == nullptr || filler2->address() == area_end()) return 0;
   DCHECK(filler2->IsFiller());
+  // The deserializer might leave behind fillers. In this case we need to
+  // iterate even further.
+  while ((filler2->address() + filler2->Size()) != area_end()) {
+    filler2 = HeapObject::FromAddress(filler2->address() + filler2->Size());
+    DCHECK(filler2->IsFiller());
+  }
   DCHECK_EQ(filler->address(), filler2->address());
 #endif  // DEBUG