fix($hmr): Support arbitrary origins in publicPath.

If the Webpack publicPath contains "http:" or "https:", treat it as the
base URL for newly-loaded
assets. Otherwise, continue to use the current window's location.

Fixes faceyspacey#25.

Author: phyllisstein

hotModuleReplacement.js

@@ -1,18 +1,16 @@
 module.exports = function(publicPath, outputFilename) {
   if (document) {
-    var origin = document.location.protocol + '//' + document.location.hostname + (document.location.port ? ':' + document.location.port: '');
-    var newHref = origin + publicPath + outputFilename
+    var newHref = publicPath.match(/https?:/g) ? new URL(outputFilename, publicPath) : new URL(outputFilename, window.location);
     var links = document.getElementsByTagName('link');
 
 	//update the stylesheet corresponding to `outputFilename`
     for (var i = 0; i < links.length; i++) {
       if (links[i].href) {
         var oldChunk = new URL(links[i].href);
-        var newChunk = new URL(newHref);
 
-        if (oldChunk.pathname === newChunk.pathname) {
+        if (oldChunk.pathname === newHref.pathname) {
           var oldSheet = links[i]
-          var url = newHref + '?' + (+new Date)
+          var url = newHref.href + '?' + (+new Date)
           var head = document.getElementsByTagName('head')[0]
           var link = document.createElement('link')