Add the most useful Apache Commons utils

compiler/java/com/google/dart/compiler/util/StringUtils.java

Index: compiler/java/com/google/dart/compiler/util/StringUtils.java
diff --git a/compiler/java/com/google/dart/compiler/util/StringUtils.java b/compiler/java/com/google/dart/compiler/util/StringUtils.java
deleted file mode 100644
index 91a1a0f7bf39402364c3c5a2f62eb4f7fb610ff4..0000000000000000000000000000000000000000
--- a/compiler/java/com/google/dart/compiler/util/StringUtils.java
+++ /dev/null
@@ -1,36 +0,0 @@
-// 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.
-package com.google.dart.compiler.util;
-
-/**
- * Utilities for {@link String}.
- */
-public class StringUtils {
-  /**
-   * The empty String <code>""</code>.
-   */
-  public static final String EMPTY = "";
-
-  /**
-   * @return the the substring before the first occurrence of a separator.
-   */
-  public static String substringBefore(String str, String separator) {
-    int index = str.indexOf(separator);
-    if (index == -1) {
-      return str;
-    }
-    return str.substring(0, index);
-  }
-
-  /**
-   * @return the substring after the first occurrence of a separator.
-   */
-  public static String substringAfter(String str, String separator) {
-    int index = str.indexOf(separator);
-    if (index == -1) {
-      return EMPTY;
-    }
-    return str.substring(index + separator.length());
-  }
-}