Add support for Page.getResourceTree

sky/framework/inspector/page-agent.sky

 <import src="/sky/framework/xmlhttprequest.sky" as="XMLHttpRequest" />
 <script>
 function Page(delegate) {
   this.delegate_ = delegate;
 }
 
 Page.prototype.enable = function() {
 };
 
 Page.prototype.canScreencast = function() {
   return {
     result: false
   };
 };
 
 Page.prototype.canEmulate = function() {
   return {
     result: false
   };
 };
 
-Page.prototype.getResourceContent = function(params, message_id) {
+Page.prototype.getResourceContent = function(params, messageId) {
   var request = new XMLHttpRequest;
   request.onload = function() {
     var message = {
       'content' : request.responseText,
     };
-    this.delegate_.sendResponse(message_id, message);
+    this.delegate_.sendResponse(messageId, message);
   }.bind(this);
   request.open("GET", params.url);
   request.send();
 
   return this.delegate_.ASYNC_RESPONSE;
 };
 
+// FIXME: ES6 has Array.from which theoretically does this.
+function arrayFromIterator(iterator) {
+  var a = [];
+  for (var e of iterator)
+    a.push(e);
+  return a;
+}
+
+// FIXME: NodeList will soon inherit from array.
+function forEachInNodeList(array, callback, scope) {
+  for (var i = 0; i < array.length; i++) {
+    callback.call(scope, array[i]);
+  }
+};
+
+function addResource(map, url, type, mimeType) {
+  // Be sure to string the url object since has(new Object)
+  // will always return false.
+  var absoluteURL = String(new URL(url, document.URL));
+  if (map.has(absoluteURL))
+    return;
+  map.set(absoluteURL, {
+    'url': String(absoluteURL),
+    'type': type,
+    'mimeType': mimeType,
+  })
+}
+
+function resourcesMapForSubtree(root_doc) {
+  var map = new Map;
+  var roots = [root_doc];
+  while (roots.length) {
+    var root = roots.pop();
+    var elements = root.querySelectorAll('*');
+    forEachInNodeList(elements, function(element) {
+      if (element.tagName == "import") {
+        // FIXME: It's no longer possible to walk into an import. :(
+        // roots.push(element.import);
+        addResource(map, element.getAttribute('src'), 'Document', 'text/html');
+      } else if (element.tagName == "img") {
+        // FIXME: Can't determine the type of an image from the DOM.
+        addResource(map, element.getAttribute('src'), 'Image', 'image/unknown');
+      }
+      if (element.shadowRoot) {
+        roots.push(element.shadowRoot);
+      }
+    });
+  }
+  return map;
+}
+
 Page.prototype.getResourceTree = function() {
   // Unclear if this is all needed, but if we don't return something here
   // the inspector hits an exception in WebInspector.ResourceTreeModel.
   return {
     "frameTree": {
       "frame": {
         "id": "1",
         "loaderId": "1",
-        "url": document.URL,
+        "url": String(document.URL),
         "mimeType": "text/html",
-        "securityOrigin": document.URL,
+        "securityOrigin": String(document.URL),
       },
-      "resources": [], // FIXME
+      "resources": arrayFromIterator(resourcesMapForSubtree(document).values()),
     }
   };
 };
 
 module.exports = Page;
 </script>