Fix dartc in optimized mode (broken in r3358).

compiler/lib/implementation/array.dart

Index: compiler/lib/implementation/array.dart
diff --git a/compiler/lib/implementation/array.dart b/compiler/lib/implementation/array.dart
index 701eae5fb0dc947c5036c658a752486ce2d7a6a2..2690982aacaca6cd287c262747f1bae76388abfb 100644
--- a/compiler/lib/implementation/array.dart
+++ b/compiler/lib/implementation/array.dart
@@ -42,19 +42,8 @@ class ListImplementation<T> implements List<T> native "Array" {
   // and coerce to false.
   bool _isFixed;
 
-  T operator[](int index) {
-    if (0 <= index && index < length) {
-      return _indexOperator(index);
-    }
-    throw new IndexOutOfRangeException(index);
-  }
-
-  void operator[]=(int index, T value) {
-    if (index < 0 || length <= index) {
-      throw new IndexOutOfRangeException(index);
-    }
-    _indexAssignOperator(index, value);
-  }
+  T operator[](int index) native;
+  void operator[]=(int index, T value) native;
 
   Iterator<T> iterator() {
     if (_isFixed) {
@@ -64,8 +53,6 @@ class ListImplementation<T> implements List<T> native "Array" {
     }
   }
 
-  T _indexOperator(int index) native;
-  void _indexAssignOperator(int index, T value) native;
   int get length() native;
   void _setLength(int length) native;
   void _add(T value) native;