[es6] Implement spec compliant ToPrimitive in the runtime.

src/execution.h

Index: src/execution.h
diff --git a/src/execution.h b/src/execution.h
index 2c07a64aaecc5409064ba1bc5eaf2f2edcf73880..d7996d1904b3098d3727d230275535f43fb9b354 100644
--- a/src/execution.h
+++ b/src/execution.h
@@ -59,10 +59,6 @@ class Execution final : public AllStatic {
                                      Handle<Object> argv[],
                                      MaybeHandle<Object>* exception_out = NULL);
 
-  // ECMA-262 9.3
-  MUST_USE_RESULT static MaybeHandle<Object> ToNumber(
-      Isolate* isolate, Handle<Object> obj);
-
   // ECMA-262 9.4
   MUST_USE_RESULT static MaybeHandle<Object> ToInteger(
       Isolate* isolate, Handle<Object> obj);
@@ -81,10 +77,6 @@ class Execution final : public AllStatic {
       Isolate* isolate, Handle<Object> obj);
 
   // ECMA-262 9.8
-  MUST_USE_RESULT static MaybeHandle<Object> ToString(
-      Isolate* isolate, Handle<Object> obj);
-
-  // ECMA-262 9.8
   MUST_USE_RESULT static MaybeHandle<Object> ToDetailString(
       Isolate* isolate, Handle<Object> obj);