Add missing properties to W3C externs.

XMLHttpRequest status codes are defined on the constructor as well as the prototype.

PiperOrigin-RevId: 321404826

Author: nreid260

externs/browser/w3c_xml.js

@@ -412,30 +412,60 @@ XMLHttpRequest.prototype.onerror;
  */
 XMLHttpRequest.UNSENT;
 
+/**
+ * @const {number}
+ * @see https://xhr.spec.whatwg.org/#states
+ */
+XMLHttpRequest.prototype.UNSENT;
+
 /**
  * @const {number}
  * @see https://xhr.spec.whatwg.org/#states
  */
 XMLHttpRequest.OPENED;
 
+/**
+ * @const {number}
+ * @see https://xhr.spec.whatwg.org/#states
+ */
+XMLHttpRequest.prototype.OPENED;
+
 /**
  * @const {number}
  * @see https://xhr.spec.whatwg.org/#states
  */
 XMLHttpRequest.HEADERS_RECEIVED;
 
+/**
+ * @const {number}
+ * @see https://xhr.spec.whatwg.org/#states
+ */
+XMLHttpRequest.prototype.HEADERS_RECEIVED;
+
 /**
  * @const {number}
  * @see https://xhr.spec.whatwg.org/#states
  */
 XMLHttpRequest.LOADING;
 
+/**
+ * @const {number}
+ * @see https://xhr.spec.whatwg.org/#states
+ */
+XMLHttpRequest.prototype.LOADING;
+
 /**
  * @const {number}
  * @see https://xhr.spec.whatwg.org/#states
  */
 XMLHttpRequest.DONE;
 
+/**
+ * @const {number}
+ * @see https://xhr.spec.whatwg.org/#states
+ */
+XMLHttpRequest.prototype.DONE;
+
 
 /**
  * @see https://xhr.spec.whatwg.org/#formdataentryvalue