[es6] Implement spec compliant ToPrimitive in the runtime.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 97d32bbe9c5b417c9060fcf287f85aaef33a82cb..826933dd9e2364bdec93be9e889e1a96ff1e9714 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -218,6 +218,7 @@ namespace internal {
   V(Boolean_string, "Boolean")                                 \
   V(callee_string, "callee")                                   \
   V(constructor_string, "constructor")                         \
+  V(default_string, "default")                                 \
   V(dot_result_string, ".result")                              \
   V(eval_string, "eval")                                       \
   V(float32x4_string, "float32x4")                             \
@@ -278,8 +279,9 @@ namespace internal {
   V(Date_string, "Date")                                       \
   V(char_at_string, "CharAt")                                  \
   V(undefined_string, "undefined")                             \
-  V(value_of_string, "valueOf")                                \
+  V(valueOf_string, "valueOf")                                 \
   V(stack_string, "stack")                                     \
+  V(toString_string, "toString")                               \
   V(toJSON_string, "toJSON")                                   \
   V(KeyedLoadMonomorphic_string, "KeyedLoadMonomorphic")       \
   V(KeyedStoreMonomorphic_string, "KeyedStoreMonomorphic")     \
@@ -353,6 +355,7 @@ namespace internal {
     Symbol.isConcatSpreadable)                                   \
   V(is_regexp_symbol, symbolIsRegExp, Symbol.isRegExp)           \
   V(iterator_symbol, symbolIterator, Symbol.iterator)            \
+  V(to_primitive_symbol, symbolToPrimitive, Symbol.toPrimitive)  \
   V(to_string_tag_symbol, symbolToStringTag, Symbol.toStringTag) \
   V(unscopables_symbol, symbolUnscopables, Symbol.unscopables)