Fix typos in String.prototype.isWellFormed/String.prototype.toWellFormed

1. String.prototype.toWellFormed's name is "toWellFormed".

2. "asserts" does not exist in the test harness, and "assert.throws"
   expects the error type first.

test/built-ins/String/prototype/isWellFormed/to-string.js

@@ -20,8 +20,8 @@ var obj = {
     }
 };
 
-asserts.throws(
+assert.throws(
-    function () { String.prototype.isWellFormed.call(obj); },
     Test262Error,
+    function () { String.prototype.isWellFormed.call(obj); },
     'coerces the receiver to a string'
 );

test/built-ins/String/prototype/toWellFormed/name.js

@@ -17,5 +17,5 @@ verifyProperty(String.prototype.toWellFormed, 'name', {
   enumerable: false,
   writable: false,
   configurable: true,
-  value: 'isWellFormed'
+  value: 'toWellFormed'
 });

test/built-ins/String/prototype/toWellFormed/to-string.js

@@ -20,8 +20,8 @@ var obj = {
     }
 };
 
-asserts.throws(
+assert.throws(
-    function () { String.prototype.toWellFormed.call(obj); },
     Test262Error,
+    function () { String.prototype.toWellFormed.call(obj); },
     'coerces the receiver to a string'
 );