Add back invalid natives that couldn't be removed due to analyzer warnings.

sdk/lib/svg/dart2js/svg_dart2js.dart

 /**
  * Scalable Vector Graphics:
  * Two-dimensional vector graphics with support for events and animation.
  *
  * For details about the features and syntax of SVG, a W3C standard,
  * refer to the
  * [Scalable Vector Graphics Specification](http://www.w3.org/TR/SVG/).
  */
 library dart.dom.svg;
 
@@ skipping 6923 matching lines @@
 // BSD-style license that can be found in the LICENSE file.
 
 
 @DocsEditable()
 @DomName('SVGElementInstanceList')
 @Unstable()
 class _ElementInstanceList extends Interceptor with ListMixin<ElementInstance>, ImmutableListMixin<ElementInstance> implements List<ElementInstance> native "SVGElementInstanceList" {
   // To suppress missing implicit constructor warnings.
   factory _ElementInstanceList._() { throw new UnsupportedError("Not supported"); }
 
+  @DomName('SVGElementInstanceList.length')
+  @DocsEditable()
+  int get length => JS("int", "#.length", this);
+
   ElementInstance operator[](int index) {
     if (JS("bool", "# >>> 0 !== # || # >= #", index,
         index, index, length))
       throw new RangeError.range(index, 0, length);
     return this.item(index);
   }
   void operator[]=(int index, ElementInstance value) {
     throw new UnsupportedError("Cannot assign element of immutable List.");
   }
   // -- start List<ElementInstance> mixins.
@@ skipping 418 matching lines @@
   @DomName('SVGVKernElement.SVGVKernElement')
   @DocsEditable()
   factory _SVGVKernElement() => _SvgElementFactoryProvider.createSvgElement_tag("vkern");
   /**
    * Constructor instantiated by the DOM when a custom element has been created.
    *
    * This can only be called by subclasses from their created constructor.
    */
   _SVGVKernElement.created() : super.created();
 }