Make instance_size immediately useful for all fixed size objects.

test/cctest/test-heap.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 
 #include <stdlib.h>
 
 #include "v8.h"
 
 #include "execution.h"
 #include "factory.h"
 #include "macro-assembler.h"
 #include "global-handles.h"
@@ skipping 18 matching lines @@
   CHECK_EQ(Heap::meta_map(), map->map());
   CHECK_EQ(type, map->instance_type());
   CHECK_EQ(instance_size, map->instance_size());
 }
 
 
 TEST(HeapMaps) {
   InitializeVM();
   CheckMap(Heap::meta_map(), MAP_TYPE, Map::kSize);
   CheckMap(Heap::heap_number_map(), HEAP_NUMBER_TYPE, HeapNumber::kSize);
-  CheckMap(Heap::fixed_array_map(), FIXED_ARRAY_TYPE, FixedArray::kHeaderSize);
-  CheckMap(Heap::string_map(), STRING_TYPE, SeqTwoByteString::kAlignedSize);
+  CheckMap(Heap::fixed_array_map(), FIXED_ARRAY_TYPE, kVariableSizeSentinel);
+  CheckMap(Heap::string_map(), STRING_TYPE, kVariableSizeSentinel);
 }
 
 
 static void CheckOddball(Object* obj, const char* string) {
   CHECK(obj->IsOddball());
   bool exc;
   Object* print_string = *Execution::ToString(Handle<Object>(obj), &exc);
   CHECK(String::cast(print_string)->IsEqualTo(CStrVector(string)));
 }
 
@@ skipping 932 matching lines @@
   Heap::CollectAllGarbage(true);
 
   // foo should no longer be in the compilation cache
   CHECK(!function->shared()->is_compiled());
   CHECK(!function->is_compiled());
   // Call foo to get it recompiled.
   CompileRun("foo()");
   CHECK(function->shared()->is_compiled());
   CHECK(function->is_compiled());
 }