Move Arrays class to private library.

runtime/lib/growable_array.dart

Index: runtime/lib/growable_array.dart
diff --git a/runtime/lib/growable_array.dart b/runtime/lib/growable_array.dart
index 38e2db66aa2009d628b16ec627ae5b05f72943f6..5759178e8609c68362b633b77af9dbea899808bf 100644
--- a/runtime/lib/growable_array.dart
+++ b/runtime/lib/growable_array.dart
@@ -48,10 +48,7 @@ class _GrowableObjectArray<T> implements List<T> {
   }
 
   void setRange(int start, int length, List<T> from, [int startFrom = 0]) {
-    if (length < 0) {
-      throw new ArgumentError("negative length $length");
-    }
-    Arrays.copy(from, startFrom, this, start, length);
+    IterableMixinWorkaround.setRangeList(this, start, length, from, startFrom);
   }
 
   void removeRange(int start, int length) {
@@ -194,12 +191,11 @@ class _GrowableObjectArray<T> implements List<T> {
   T max([int compare(T a, T b)]) => IterableMixinWorkaround.max(this, compare);
 
   int indexOf(T element, [int start = 0]) {
-    return Arrays.indexOf(this, element, start, length);
+    return IterableMixinWorkaround.indexOfList(this, element, start);
   }
 
   int lastIndexOf(T element, [int start = null]) {
-    if (start == null) start = length - 1;
-    return Arrays.lastIndexOf(this, element, start);
+    return IterableMixinWorkaround.lastIndexOfList(this, element, start);
   }
 
   void _grow(int new_length) {