Implement List<T> operations on dom types via manual mixins.

client/dom/src/_Lists.dart

Index: client/dom/src/_Lists.dart
diff --git a/client/dom/src/_Lists.dart b/client/dom/src/_Lists.dart
index e75b06a0bdc55be01e25720ba13968d798be99d3..002c1fc671ac02ecf348b2d03ad252a8e911931a 100644
--- a/client/dom/src/_Lists.dart
+++ b/client/dom/src/_Lists.dart
@@ -46,4 +46,23 @@ class _Lists {
     }
     return -1;
   }
+
+  /**
+   * Returns a sub list copy of this list, from [start] to
+   * [:start + length:].
+   * Returns an empty list if [length] is 0.
+   * Throws an [IllegalArgumentException] if [length] is negative.
+   * Throws an [IndexOutOfRangeException] if [start] or
+   * [:start + length:] are out of range.
+   */
+  static List getRange(List a, int start, int length, List accumulator) {
+    if (length < 0) throw new IllegalArgumentException('length');
+    if (start < 0) throw new IndexOutOfRangeException(start);
+    int end = start + length;
+    if (end > a.length) throw new IndexOutOfRangeException(end);
+    for (int i = start; i < end; i++) {
+      accumulator.add(a[i]);
+    }
+    return accumulator;
+  }
 }