[runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

test/mjsunit/harmony/to-string.js

+// Copyright 2015 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.
+
+// Flags: --allow-natives-syntax
+
+assertEquals("1", %ToString(1));
+assertEquals("1", %_ToString(1));
+
+assertEquals("0.5", %ToString(.5));
+assertEquals("0.5", %_ToString(.5));
+
+assertEquals("null", %ToString(null));
+assertEquals("null", %_ToString(null));
+
+assertEquals("true", %ToString(true));
+assertEquals("true", %_ToString(true));
+
+assertEquals("false", %ToString(false));
+assertEquals("false", %_ToString(false));
+
+assertEquals("undefined", %ToString(undefined));
+assertEquals("undefined", %_ToString(undefined));
+
+assertEquals("random text", %ToString("random text"));
+assertEquals("random text", %_ToString("random text"));
+
+assertThrows(function() { %ToString(Symbol.toPrimitive) }, TypeError);
+assertThrows(function() { %_ToString(Symbol.toPrimitive) }, TypeError);
+
+var a = { toString: function() { return "xyz" }};
+assertEquals("xyz", %ToString(a));
+assertEquals("xyz", %_ToString(a));
+
+var b = { valueOf: function() { return 42 }};
+assertEquals("[object Object]", %ToString(b));
+assertEquals("[object Object]", %_ToString(b));
+
+var c = {
+  toString: function() { return "x"},
+  valueOf: function() { return 123 }
+};
+assertEquals("x", %ToString(c));
+assertEquals("x", %_ToString(c));
+
+var d = {
+  [Symbol.toPrimitive]: function(hint) { return hint }
+};
+assertEquals("string", %ToString(d));
+assertEquals("string", %_ToString(d));