Fix copy-on-write assert by setting the new array map early.

src/heap.cc

 // Copyright 2010 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 3187 matching lines @@
   // Use the general function if we're forced to always allocate.
   if (always_allocate()) return AllocateFixedArray(length, TENURED);
   // Allocate the raw data for a fixed array.
   int size = FixedArray::SizeFor(length);
   return size <= kMaxObjectSizeInNewSpace
       ? new_space_.AllocateRaw(size)
       : lo_space_->AllocateRawFixedArray(size);
 }
 
 
-Object* Heap::CopyFixedArray(FixedArray* src) {
+Object* Heap::CopyFixedArrayWithMap(FixedArray* src, Map* map) {
   int len = src->length();
   Object* obj = AllocateRawFixedArray(len);
   if (obj->IsFailure()) return obj;
   if (Heap::InNewSpace(obj)) {
     HeapObject* dst = HeapObject::cast(obj);
-    CopyBlock(dst->address(), src->address(), FixedArray::SizeFor(len));
+    dst->set_map(map);
+    CopyBlock(dst->address() + kPointerSize,
+              src->address() + kPointerSize,
+              FixedArray::SizeFor(len) - kPointerSize);
     return obj;
   }
-  HeapObject::cast(obj)->set_map(src->map());
+  HeapObject::cast(obj)->set_map(map);
   FixedArray* result = FixedArray::cast(obj);
   result->set_length(len);
 
   // Copy the content
   AssertNoAllocation no_gc;
   WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
   for (int i = 0; i < len; i++) result->set(i, src->get(i), mode);
   return result;
 }
 
@@ skipping 1737 matching lines @@
 void ExternalStringTable::TearDown() {
   new_space_strings_.Free();
   old_space_strings_.Free();
 }
 
 
 List<Object*> ExternalStringTable::new_space_strings_;
 List<Object*> ExternalStringTable::old_space_strings_;
 
 } }  // namespace v8::internal