Switch custom XMLHttpRequest bindings over to new-style ExceptionState.

LayoutTests/fast/js/script-tests/dfg-custom-getter-throw.js

 description(
 "Tests that DFG custom getter caching does not break the world if the getter throws an exception."
 );
 
 function foo(x) {
     return x.responseText;
 }
 
 function bar(binary) {
     var x = new XMLHttpRequest();
     x.open("GET", "http://foo.bar.com/");
     if (binary)
         x.responseType = "arraybuffer";
     try {
         return "Returned result: " + foo(x);
     } catch (e) {
         return "Threw exception: " + e;
     }
 }
 
 for (var i = 0; i < 200; ++i) {
-    shouldBe("bar(i >= 100)", i >= 100 ? "\"Threw exception: InvalidStateError: Failed to read the 'responseText' property from 'XMLHttpRequest': the value is only accessible if the object's 'responseType' is '' or 'text' (was 'arraybuffer').\"" : "\"Returned result: \"");
+    shouldBe("bar(i >= 100)", i >= 100 ? "\"Threw exception: InvalidStateError: Failed to read the 'responseText' property from 'XMLHttpRequest': The value is only accessible if the object's 'responseType' is '' or 'text' (was 'arraybuffer').\"" : "\"Returned result: \"");
 }