Revert "Move Arrays class to private library."

sdk/lib/_internal/compiler/implementation/lib/js_helper.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
index f9a3af7c6ad148cf9a58ef529b71e0abd36bb8bc..353c7880e50417772036d572c9ede59b92f1c3cc 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
@@ -561,6 +561,32 @@ ioore(index) {
   throw new RangeError.value(index);
 }
 
+listInsertRange(receiver, start, length, initialValue) {
+  if (length == 0) {
+    return;
+  }
+  if (length is !int) throw new ArgumentError(length);
+  if (length < 0) throw new ArgumentError(length);
+  if (start is !int) throw new ArgumentError(start);
+
+  var receiverLength = JS('num', r'#.length', receiver);
+  if (start < 0 || start > receiverLength) {
+    throw new RangeError.value(start);
+  }
+  receiver.length = receiverLength + length;
+  Arrays.copy(receiver,
+              start,
+              receiver,
+              start + length,
+              receiverLength - start);
+  if (initialValue != null) {
+    for (int i = start; i < start + length; i++) {
+      receiver[i] = initialValue;
+    }
+  }
+  receiver.length = receiverLength + length;
+}
+
 stringLastIndexOfUnchecked(receiver, element, start)
   => JS('int', r'#.lastIndexOf(#, #)', receiver, element, start);