Change IllegalArgumentException to ArgumentError.

lib/html/templates/html/impl/impl_Element.darttemplate

Index: lib/html/templates/html/impl/impl_Element.darttemplate
diff --git a/lib/html/templates/html/impl/impl_Element.darttemplate b/lib/html/templates/html/impl/impl_Element.darttemplate
index 2b78504b5ab88b794ce226f09c96ba4e9267c262..2bb8351d292fd91f66b11648adc67acab887a32a 100644
--- a/lib/html/templates/html/impl/impl_Element.darttemplate
+++ b/lib/html/templates/html/impl/impl_Element.darttemplate
@@ -807,7 +807,7 @@ $if DART2JS
         this.parent.insertBefore(node, this.nextNode);
         break;
       default:
-        throw new IllegalArgumentException("Invalid position ${where}");
+        throw new ArgumentError("Invalid position ${where}");
     }
   }
 $else
@@ -864,7 +864,7 @@ class _ElementFactoryProvider {
       // only contains a head or body element.
       element = temp.elements[tag == 'head' ? 0 : 1];
     } else {
-      throw new IllegalArgumentException('HTML had ${temp.elements.length} '
+      throw new ArgumentError('HTML had ${temp.elements.length} '
           'top level elements but 1 expected');
     }
     element.remove();