Add assertion to UniqueValueId constructor.

src/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1396 matching lines @@
     roots_[kEmptyScriptRootIndex] = script;
   }
 
   void public_set_store_buffer_top(Address* top) {
     roots_[kStoreBufferTopRootIndex] = reinterpret_cast<Smi*>(top);
   }
 
   // Generated code can embed this address to get access to the roots.
   Object** roots_array_start() { return roots_; }
 
+#ifdef DEBUG
+  bool IsInRootsArray(Object** handle) {
+    return roots_ <= handle && handle < roots_ + Heap::kStrongRootListLength;
+  }
+#endif
+
   Address* store_buffer_top_address() {
     return reinterpret_cast<Address*>(&roots_[kStoreBufferTopRootIndex]);
   }
 
   // Get address of native contexts list for serialization support.
   Object** native_contexts_list_address() {
     return &native_contexts_list_;
   }
 
 #ifdef VERIFY_HEAP
@@ skipping 1613 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_