Teach XHR how to handle relative urls.

sky/framework/xmlhttprequest.sky

 <import src="/mojo/public/sky/core.sky" as="core" />
 <import src="/mojo/public/sky/unicode.sky" as="unicode" />
 <import src="/mojo/services/public/interfaces/network/network_service.mojom.sky" as="net" />
 <import src="/mojo/services/public/interfaces/network/url_loader.mojom.sky" as="loader" />
 <import src="shell.sky" as="shell" />
 <script>
+// XHR keeps itself alive.
+var outstandingRequests = new Set();

[esprehn, 2014/11/18 02:06:24]

Why do you need this? I thought the Mojo JS stuff abarth@ and I worked on solved
this.

[abarth-chromium, 2014/11/18 02:11:59]

It doesn't.  :(

We can make the waiting callbacks strong, which would solve the problem.  (See
https://codereview.chromium.org/734633004/).

Another option is to have the static set at the bindings layer...

[esprehn, 2014/11/18 02:15:49]

Fixing this with one off Sets seems like a mistake, there's going to be so many
bugs.

+
 function XMLHttpRequest() {
   this.networkService_ = shell.connectToService(
     "mojo:network_service", net.NetworkService);
   this.request_ = null;
   this.loader_ = null;
   this.responseText = null;
   this.headers_ = new Map();
 };
 
 XMLHttpRequest.prototype.onload = function() { };
 XMLHttpRequest.prototype.onerror = function(error) { };
 
 XMLHttpRequest.prototype.open = function(method, url) {
   this.request_ = new loader.URLRequest();
-  this.request_.url = url;
+  this.request_.url = new URL(url, document.URL);
   this.request_.method = method;
   this.request_.auto_follow_redirects = true;
   this.headers_.clear();
 };
 
 XMLHttpRequest.prototype.setRequestHeader = function(header, value) {
   this.headers_.set(header, value);
 };
 
 XMLHttpRequest.prototype.send = function() {
   var requestHeaders = [];
   this.headers_.forEach(function(value, key) {
     requestHeaders.push(key + ': ' + value);
   });
   this.request_.headers = requestHeaders;
 
   // FIXME: Factor this into the JS bindings.
   var pipe = new core.createMessagePipe();
   this.networkService_.createURLLoader(pipe.handle1);
   this.loader_ = shell.wrapHandle(pipe.handle0, loader.URLLoader);
 
   var self = this;
+  outstandingRequests.add(this);
   this.loader_.start(this.request_).then(function(result) {
     return core.drainData(result.response.body).then(function(result) {
+      outstandingRequests.delete(self);
       self.responseText = unicode.decodeUtf8String(new Uint8Array(result.buffer));
       self.onload();
     });
   }).catch(function(error) {
+    outstandingRequests.delete(self);
     self.onerror(error);
   });
 };
 
 module.exports = XMLHttpRequest;
 </script>