dart2js: Always generate functions for rti substitutions.

sdk/lib/_internal/compiler/js_lib/js_rti.dart

Index: sdk/lib/_internal/compiler/js_lib/js_rti.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/js_rti.dart b/sdk/lib/_internal/compiler/js_lib/js_rti.dart
index 5293613a058c42d52e16a1e0e640f56cb58ff761..2cf4b4826b467721cc46084a6e12aec4f6340ca3 100644
--- a/sdk/lib/_internal/compiler/js_lib/js_rti.dart
+++ b/sdk/lib/_internal/compiler/js_lib/js_rti.dart
@@ -232,12 +232,9 @@ Type getRuntimeType(var object) {
  */
 substitute(var substitution, var arguments) {
   assert(isNull(substitution) ||
-         isJsArray(substitution) ||
          isJsFunction(substitution));
   assert(isNull(arguments) || isJsArray(arguments));
-  if (isJsArray(substitution)) {
-    arguments = substitution;
-  } else if (isJsFunction(substitution)) {
+  if (isJsFunction(substitution)) {
     substitution = invoke(substitution, arguments);
     if (isJsArray(substitution)) {
       arguments = substitution;