Add checks to the marking queue

src/heap/mark-compact.h

 // Copyright 2012 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.
 
 #ifndef V8_HEAP_MARK_COMPACT_H_
 #define V8_HEAP_MARK_COMPACT_H_
 
 #include "src/base/bits.h"
 #include "src/heap/spaces.h"
 
@@ skipping 150 matching lines @@
 
   void ClearOverflowed() { overflowed_ = false; }
 
   void SetOverflowed() { overflowed_ = true; }
 
   // Push the (marked) object on the marking stack if there is room,
   // otherwise mark the object as overflowed and wait for a rescan of the
   // heap.
   INLINE(void PushBlack(HeapObject* object)) {
     DCHECK(object->IsHeapObject());
+    // TODO(jochen): Remove again before we branch for 4.2.
+    CHECK(object->IsHeapObject() && object->map()->IsMap());
     if (IsFull()) {
       Marking::BlackToGrey(object);
       MemoryChunk::IncrementLiveBytesFromGC(object->address(), -object->Size());
       SetOverflowed();
     } else {
       array_[top_] = object;
       top_ = ((top_ + 1) & mask_);
     }
   }
 
   INLINE(void PushGrey(HeapObject* object)) {
     DCHECK(object->IsHeapObject());
+    // TODO(jochen): Remove again before we branch for 4.2.
+    CHECK(object->IsHeapObject() && object->map()->IsMap());
     if (IsFull()) {
       SetOverflowed();
     } else {
       array_[top_] = object;
       top_ = ((top_ + 1) & mask_);
     }
   }
 
   INLINE(HeapObject* Pop()) {
     DCHECK(!IsEmpty());
@@ skipping 759 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_MARK_COMPACT_H_