[heap] Fix debug check in ShrinkToHighWaterMark

src/heap/spaces.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/spaces.h"
 
 #include <utility>
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
@@ skipping 777 matching lines @@
 
 #ifdef DEBUG
   // Check the the filler is indeed the last filler on the page.
   HeapObjectIterator it(this);
   HeapObject* filler2 = nullptr;
   for (HeapObject* obj = it.Next(); obj != nullptr; obj = it.Next()) {
     filler2 = HeapObject::FromAddress(obj->address() + obj->Size());
   }
   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
 
   size_t unused = RoundDown(
       static_cast<size_t>(area_end() - filler->address() - FreeSpace::kSize),
       base::OS::CommitPageSize());
   if (unused > 0) {
     if (FLAG_trace_gc_verbose) {
       PrintIsolate(heap()->isolate(), "Shrinking page %p: end %p -> %p\n",
                    reinterpret_cast<void*>(this),
@@ skipping 2421 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 }  // namespace internal
 }  // namespace v8