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

sdk/lib/svg/dartium/svg_dartium.dart

Index: sdk/lib/svg/dartium/svg_dartium.dart
diff --git a/sdk/lib/svg/dartium/svg_dartium.dart b/sdk/lib/svg/dartium/svg_dartium.dart
index 0a7963ab56a51fcf4e0fb5228539fc08ea490c64..ebfc7e4b1e129615525367599024b1fb614c1968 100644
--- a/sdk/lib/svg/dartium/svg_dartium.dart
+++ b/sdk/lib/svg/dartium/svg_dartium.dart
@@ -7762,6 +7762,10 @@ class _ElementInstanceList extends NativeFieldWrapperClass2 with ListMixin<Eleme
   // To suppress missing implicit constructor warnings.
   factory _ElementInstanceList._() { throw new UnsupportedError("Not supported"); }
 
+  @DomName('SVGElementInstanceList.length')
+  @DocsEditable()
+  int get length => _blink.Native_SVGElementInstanceList_length_Getter(this);
+
   ElementInstance operator[](int index) {
     if (index < 0 || index >= length)
       throw new RangeError.range(index, 0, length);