Attempt to fix page-agent-get-resource-tree on the bot

sky/tests/inspector/page-agent-get-resource-tree.sky

Index: sky/tests/inspector/page-agent-get-resource-tree.sky
diff --git a/sky/tests/inspector/page-agent-get-resource-tree.sky b/sky/tests/inspector/page-agent-get-resource-tree.sky
index 99646824ed3f06d12c45ef91e09a8f50c787397e..cc5e113d8ed8ffe85d2c5e15257a1ff279e4b52a 100644
--- a/sky/tests/inspector/page-agent-get-resource-tree.sky
+++ b/sky/tests/inspector/page-agent-get-resource-tree.sky
@@ -4,6 +4,11 @@
 <import src="/sky/framework/inspector/page-agent.sky" as="PageAgent" />
 <img src='does_not_exist.jpg' />
 <script>
+// This is to avoid hard-coding the hostname and port number in the tests.
+function absoluteURL(url) {
+  return String(new URL(url, document.URL));
+}
+
 describe('PageAgent.getResourceTree', function() {
   it('should dump the current resource tree', function() {
     var pageAgent = new PageAgent();
@@ -14,24 +19,24 @@ describe('PageAgent.getResourceTree', function() {
         "frame": {
           "id": "1",
           "loaderId": "1",
-          "url": "http://127.0.0.1:8000/sky/tests/inspector/page-agent-get-resource-tree.sky",
+          "url": absoluteURL("/sky/tests/inspector/page-agent-get-resource-tree.sky"),
           "mimeType": "text/html",
-          "securityOrigin": "http://127.0.0.1:8000/sky/tests/inspector/page-agent-get-resource-tree.sky"
+          "securityOrigin": absoluteURL("/sky/tests/inspector/page-agent-get-resource-tree.sky")
         },
         "resources": [{
-          "url": "http://127.0.0.1:8000/sky/tests/resources/chai.sky",
+          "url": absoluteURL("/sky/tests/resources/chai.sky"),
           "type": "Document",
           "mimeType": "text/html"
         }, {
-          "url": "http://127.0.0.1:8000/sky/tests/resources/mocha.sky",
+          "url": absoluteURL("/sky/tests/resources/mocha.sky"),
           "type": "Document",
           "mimeType": "text/html"
         }, {
-          "url": "http://127.0.0.1:8000/sky/framework/inspector/page-agent.sky",
+          "url": absoluteURL("/sky/framework/inspector/page-agent.sky"),
           "type": "Document",
           "mimeType": "text/html"
         }, {
-          "url": "http://127.0.0.1:8000/sky/tests/inspector/does_not_exist.jpg",
+          "url": absoluteURL("/sky/tests/inspector/does_not_exist.jpg"),
           "type": "Image",
           "mimeType": "image/unknown"
         }]