[heap] Assert that there's no recodred slot corresponding to unboxed double field.

src/heap/slot-set.h

 // Copyright 2016 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_SLOT_SET_H
 #define V8_SLOT_SET_H
 
 #include <map>
 #include <stack>
 
@@ skipping 48 matching lines @@
     if (current_bucket == nullptr) {
       current_bucket = AllocateBucket();
       bucket[bucket_index].SetValue(current_bucket);
     }
     if (!(current_bucket[cell_index].Value() & (1u << bit_index))) {
       current_bucket[cell_index].SetBit(bit_index);
     }
   }
 
   // The slot offset specifies a slot at address page_start_ + slot_offset.
+  // Returns true if the set contains the slot.
+  bool Contains(int slot_offset) {
+    int bucket_index, cell_index, bit_index;
+    SlotToIndices(slot_offset, &bucket_index, &cell_index, &bit_index);
+    base::AtomicValue<uint32_t>* current_bucket = bucket[bucket_index].Value();
+    if (current_bucket == nullptr) {
+      return false;
+    }
+    return (current_bucket[cell_index].Value() & (1u << bit_index)) != 0;
+  }
+
+  // The slot offset specifies a slot at address page_start_ + slot_offset.
   void Remove(int slot_offset) {
     int bucket_index, cell_index, bit_index;
     SlotToIndices(slot_offset, &bucket_index, &cell_index, &bit_index);
     base::AtomicValue<uint32_t>* current_bucket = bucket[bucket_index].Value();
     if (current_bucket != nullptr) {
       uint32_t cell = current_bucket[cell_index].Value();
       if (cell) {
         uint32_t bit_mask = 1u << bit_index;
         if (cell & bit_mask) {
           current_bucket[cell_index].ClearBit(bit_index);
@@ skipping 443 matching lines @@
   Address page_start_;
   base::AtomicValue<Chunk*> chunk_;
   base::Mutex to_be_freed_chunks_mutex_;
   std::stack<Chunk*> to_be_freed_chunks_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_SLOT_SET_H