Fix migration checks and extend them to the Scavenger.

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 1373 matching lines @@
 
   // Checks whether an address/object in a space.
   // Currently used by tests, serialization and heap verification only.
   bool InSpace(Address addr, AllocationSpace space);
   bool InSpace(HeapObject* value, AllocationSpace space);
 
   // Finds out which space an object should get promoted to based on its type.
   inline OldSpace* TargetSpace(HeapObject* object);
   static inline AllocationSpace TargetSpaceId(InstanceType type);
 
+  // Checks whether the given object is allowed to be migrated from it's
+  // current space into the given destination space. Used for debugging.
+  inline bool AllowedToBeMigrated(HeapObject* object, AllocationSpace dest);
+
   // Sets the stub_cache_ (only used when expanding the dictionary).
   void public_set_code_stubs(UnseededNumberDictionary* value) {
     roots_[kCodeStubsRootIndex] = value;
   }
 
   // Support for computing object sizes for old objects during GCs. Returns
   // a function that is guaranteed to be safe for computing object sizes in
   // the current GC phase.
   HeapObjectCallback GcSafeSizeOfOldObjectFunction() {
     return gc_safe_size_of_old_object_;
@@ skipping 1640 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_