Revert "Removes dartc reliance on its own libraries, now can be targeted at any implementation's li…

compiler/lib/implementation/string_base.dart

+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class StringBase {
+  static String createFromCharCodes(List<int> charCodes) native;
+
+  static String join(List<String> strings, String separator) {
+    String s = "";
+    for (int i = 0; i < strings.length; i++) {
+      if (i > 0) {
+        s = s.concat(separator);
+      }
+      s = s.concat(strings[i]);
+    }
+    return s;
+  }
+
+  static String concatAll(List<String> strings) {
+    return join(strings, "");
+  }
+
+}