Add constructors for SVG elements and remove static factory providers for html elements.

tests/html/svgelement_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library SVGElementTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 import 'dart:svg';
 
@@ skipping 134 matching lines @@
     testConstructor('text', (e) => e is SVGTextElement);
     testConstructor('textPath', (e) => e is SVGTextPathElement);
     testConstructor('title', (e) => e is SVGTitleElement);
     testConstructor('use', (e) => e is SVGUseElement);
     testConstructor('view', (e) => e is SVGViewElement);
   });
 
   group('outerHTML', () {
     test('outerHTML', () {
       final el = new SVGSVGElement();
-      el.elements.add(new SVGElement.tag("circle"));
-      el.elements.add(new SVGElement.tag("path"));
+      el.elements.add(new SVGCircleElement());
+      el.elements.add(new SVGPathElement());
       expect(el.outerHTML,
           '<svg version="1.1"><circle></circle><path></path></svg>');
     });
   });
 
   group('innerHTML', () {
     test('get', () {
       final el = new SVGSVGElement();
-      el.elements.add(new SVGElement.tag("circle"));
-      el.elements.add(new SVGElement.tag("path"));
+      el.elements.add(new SVGCircleElement());
+      el.elements.add(new SVGPathElement());
       expect(el.innerHTML, '<circle></circle><path></path>');
     });
 
     test('set', () {
       final el = new SVGSVGElement();
-      el.elements.add(new SVGElement.tag("circle"));
-      el.elements.add(new SVGElement.tag("path"));
+      el.elements.add(new SVGCircleElement());
+      el.elements.add(new SVGPathElement());
       el.innerHTML = '<rect></rect><a></a>';
       expect(_nodeStrings(el.elements), ["rect", "a"]);
     });
   });
 
   group('elementget', () {
     test('get', () {
       final el = new SVGElement.svg("""
 <svg version="1.1">
   <circle></circle>
   <path></path>
   text
 </svg>""");
       expect(_nodeStrings(el.elements), ["circle", "path"]);
     });
   });
 
   group('elementset', () {
     test('set', () {
       final el = new SVGSVGElement();
       el.elements = [new SVGElement.tag("circle"), new SVGElement.tag("path")];
       expect(el.innerHTML, '<circle></circle><path></path>');
     });
   });
 }