Revert "Make EfficientLength public, as EfficientLengthIterable."

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

Index: sdk/lib/_internal/compiler/js_lib/js_array.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/js_array.dart b/sdk/lib/_internal/compiler/js_lib/js_array.dart
index bef50266441e2b483cb692e06bf9e504b641d590..d706b7512780c72e7bc400f4396d384557c79c05 100644
--- a/sdk/lib/_internal/compiler/js_lib/js_array.dart
+++ b/sdk/lib/_internal/compiler/js_lib/js_array.dart
@@ -124,7 +124,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
   void insertAll(int index, Iterable<E> iterable) {
     checkGrowable('insertAll');
     RangeError.checkValueInInterval(index, 0, this.length, "index");
-    if (iterable is! EfficientLengthIterable) {
+    if (iterable is! EfficientLength) {
       iterable = iterable.toList();
     }
     int insertionLength = iterable.length;
@@ -439,7 +439,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
   void replaceRange(int start, int end, Iterable<E> replacement) {
     checkGrowable('replace range');
     RangeError.checkValidRange(start, end, this.length);
-    if (replacement is! EfficientLengthIterable) {
+    if (replacement is! EfficientLength) {
       replacement = replacement.toList();
     }
     int removeLength = end - start;