Implement List.getRange.

compiler/lib/implementation/arrays.dart

Index: compiler/lib/implementation/arrays.dart
===================================================================
--- compiler/lib/implementation/arrays.dart	(revision 402)
+++ compiler/lib/implementation/arrays.dart	(working copy)
@@ -63,4 +63,16 @@
     }
     return -1;
   }
+
+  static void rangeCheck(Array a, int start, int length) {
+    if (length < 0) {
+      throw new IllegalArgumentException("negative length $length");
+    }
+    if (start < 0 || start > a.length) {
+      throw new IndexOutOfRangeException(start);
+    }
+    if (start + length > a.length) {
+      throw new IndexOutOfRangeException(start + length);
+    }
+  }
 }