Move dom-serializer.sky to dom_serializer.dart (and clean up some analyizer errors)

sky/tests/resources/dom_serializer.dart

-<!--
 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
--->
-<script>
 import "dart:sky";
 
 final kEntityMap = new Map.fromIterable([
   ['\u00a0', '&nbsp;'],
   ['&', '&amp;'],
   ['<', '&lt;'],
   ['>', '&gt;'],
   ['"', '&quot;'],
 ], key: (item) => item[0], value: (item) => item[1]);
 
@@ skipping 18 matching lines @@
     buffer += ' ';
     buffer += attribute.name;
     buffer += '="';
     buffer += escapeText(attribute.value, kAttributeEscapePattern);
     buffer += '"';
   }
 
   return buffer;
 }
 
-Node getFirstChild(Node node) {
+Node getFirstChild(ParentNode node) {
   if (node is HTMLTemplateElement)
     return node.content.firstChild;
   return node.firstChild;
 }
 
-Node getLastChild(Node node) {
+Node getLastChild(ParentNode node) {
   if (node is HTMLTemplateElement)
     return node.content.lastChild;
   return node.lastChild;
 }
 
-String serializeChildren(Node node, int depth) {
+String serializeChildren(ParentNode node, int depth) {
   String buffer = '';
   Node firstChild = getFirstChild(node);
   Node lastChild = getLastChild(node);
   if (firstChild is Element && depth != 0)
     buffer += '\n' + (kIndent * depth);
   for (Node child = firstChild; child != null; child = child.nextSibling) {
     buffer += serializeNode(child, depth);
     if (child is Element && child.nextSibling is Element)
       buffer += '\n' + (kIndent * depth);
   }
   if (lastChild is Element) {
     buffer += '\n';
     if (depth != 0)
       buffer += kIndent * (depth - 1);
   }
   return buffer;
 }
 
 String serializeElement(Element element, int depth) {
   String buffer = '<' + element.tagName + serializeAttributes(element) + '>';
   buffer += serializeChildren(element, depth + 1);
   buffer += '</' + element.tagName + '>';
   return buffer;
 }
 
-String serializeText(Node node) {
+String serializeText(Text node) {
   Node parent = node.parentNode;
   if (parent != null && (parent is HTMLScriptElement || parent is HTMLStyleElement))
     return node.data;
   return escapeText(node.data, kTextEscapePattern);
 }
 
 String serializeNode(Node node, [int depth = 0]) {
   if (node is Text)
     return serializeText(node);
   if (node is Element)
     return serializeElement(node, depth);
   if (node is Document || node is ShadowRoot)
     return serializeChildren(node, depth);
-  throw new Error('Cannot serialize node');
+  throw new Exception('Cannot serialize node');
 }
-</script>