Special case the "empty string" root so it doesn't constantly jump around

src/heap/heap.cc

 // Copyright 2012 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.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 2494 matching lines @@
 const Heap::StringTypeTable Heap::string_type_table[] = {
 #define STRING_TYPE_ELEMENT(type, size, name, camel_name) \
   { type, size, k##camel_name##MapRootIndex }             \
   ,
     STRING_TYPE_LIST(STRING_TYPE_ELEMENT)
 #undef STRING_TYPE_ELEMENT
 };
 
 
 const Heap::ConstantStringTable Heap::constant_string_table[] = {
+    {"", kempty_stringRootIndex},
 #define CONSTANT_STRING_ELEMENT(name, contents) \
   { contents, k##name##RootIndex }              \
   ,
     INTERNALIZED_STRING_LIST(CONSTANT_STRING_ELEMENT)
 #undef CONSTANT_STRING_ELEMENT
 };
 
 
 const Heap::StructTable Heap::struct_table[] = {
 #define STRUCT_TABLE_ELEMENT(NAME, Name, name)        \
@@ skipping 3840 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 }
 }  // namespace v8::internal