Add supported checks to the SVG library, and library cleanup.

tests/html/svg_2_test.dart

-library SVG2Test;
-import '../../pkg/unittest/lib/unittest.dart';
-import '../../pkg/unittest/lib/html_config.dart';
-import 'dart:html';
-import 'dart:svg' as svg;
-
-// Test that SVG elements explicitly implement the IDL interfaces (is-checks
-// only, see SVGTest3 for behavioural tests).
-
-main() {
-
-  insertTestDiv() {
-    var element = new Element.tag('div');
-    element.innerHtml = r'''
-<svg id='svg1' width='200' height='100'>
-<rect id='rect1' x='10' y='20' width='130' height='40' rx='5'fill='blue'></rect>
-</svg>
-''';
-    document.body.nodes.add(element);
-    return element;
-  }
-
-  useHtmlConfiguration();
-
-  var isElement = predicate((x) => x is Element, 'is an Element');
-  var isSvgElement = predicate((x) => x is svg.SvgElement, 'is a SvgElement');
-  var isSvgSvgElement =
-      predicate((x) => x is svg.SvgSvgElement, 'is a SvgSvgElement');
-  var isNode = predicate((x) => x is Node, 'is a Node');
-  var isSvgTests = predicate((x) => x is svg.Tests, 'is a svg.Tests');
-  var isSvgLangSpace = predicate((x) => x is svg.LangSpace, 'is a svg.LangSpace');
-  var isSvgExternalResourcesRequired =
-      predicate((x) => x is svg.ExternalResourcesRequired,
-          'is a svg.ExternalResourcesRequired');
-  var isSvgTransformable =
-      predicate((x) => x is svg.Transformable, 'is a svg.Transformable');
-  var isSvgLocatable =
-      predicate((x) => x is svg.Locatable, 'is a svg.Locatable');
-  var isSvgNumber = predicate((x) => x is svg.Number, 'is a svg.Number');
-  var isSvgRect = predicate((x) => x is svg.Rect, 'is a svg.Rect');
-
-  test('rect_isChecks', () {
-      var div = insertTestDiv();
-      var r = document.query('#rect1');
-
-      // Direct inheritance chain
-      expect(r, isSvgElement);
-      expect(r, isElement);
-      expect(r, isNode);
-
-      // Other implemented interfaces.
-      expect(r, isSvgTests);
-      expect(r, isSvgLangSpace);
-      expect(r, isSvgExternalResourcesRequired);
-      expect(r, isSvgTransformable);
-      expect(r, isSvgLocatable);
-
-      // Interfaces not implemented.
-      expect(r, isNot(isSvgNumber));
-      expect(r, isNot(isSvgRect));
-      expect(r, isNot(isSvgSvgElement));
-
-      div.remove();
-    });
-}