Check the slots being adding to the SlotsBuffer.

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 248 matching lines @@
       : idx_(0), chain_length_(1), next_(next_buffer) {
     if (next_ != NULL) {
       chain_length_ = next_->chain_length_ + 1;
     }
   }
 
   ~SlotsBuffer() {}
 
   void Add(ObjectSlot slot) {
     DCHECK(0 <= idx_ && idx_ < kNumberOfElements);
+#ifdef DEBUG
+    if (slot >= reinterpret_cast<ObjectSlot>(NUMBER_OF_SLOT_TYPES)) {
+      DCHECK_NOT_NULL(*slot);
+    }
+#endif
     slots_[idx_++] = slot;
   }
 
   enum SlotType {
     EMBEDDED_OBJECT_SLOT,
     RELOCATED_CODE_OBJECT,
     CODE_TARGET_SLOT,
     CODE_ENTRY_SLOT,
     DEBUG_TARGET_SLOT,
     JS_RETURN_SLOT,
@@ skipping 677 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_MARK_COMPACT_H_