Make helper utils in String private.

Change-Id: I90e39f78c6deb978804084704410076609f41f66
diff --git a/user/super/com/google/gwt/emul/java/lang/String.java b/user/super/com/google/gwt/emul/java/lang/String.java
index 6bf9e92..37cab11 100644
--- a/user/super/com/google/gwt/emul/java/lang/String.java
+++ b/user/super/com/google/gwt/emul/java/lang/String.java
@@ -615,7 +615,7 @@
     return jsArrayString;
   }
 
-  public native String[] split0(String regex, int maxMatch) /*-{
+  private native String[] split0(String regex, int maxMatch) /*-{
     // The compiled regular expression created from the string
     var compiled = new RegExp(regex, "g");
     // the Javascipt array to hold the matches prior to conversion