7175133: jinfo failed to get system properties after 6924259

Summary: String offset and count fields as fix of 6924259 were removed, and become optional. SA still use offset and count fields to read String contents and failed. Fix if they exist, use them other then use value field only to read, this keeps consistent with the changes in 6924259.
Reviewed-by: dholmes, mikael
Contributed-by: yumin.qi@oracle.com

agent/src/share/classes/sun/jvm/hotspot/oops/OopUtilities.java

 /*
- * Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -141,18 +141,19 @@ public class OopUtilities implements /* imports */ JVMTIThreadState {
   public static String stringOopToString(Oop stringOop) {
     if (offsetField == null) {
       InstanceKlass k = (InstanceKlass) stringOop.getKlass();
-      offsetField = (IntField) k.findField("offset", "I");
-      countField  = (IntField) k.findField("count",  "I");
+      offsetField = (IntField) k.findField("offset", "I");   // optional
+      countField  = (IntField) k.findField("count",  "I");   // optional
       valueField  = (OopField) k.findField("value",  "[C");
       if (Assert.ASSERTS_ENABLED) {
-        Assert.that(offsetField != null &&
-                    countField != null &&
-                    valueField != null, "must find all java.lang.String fields");
+         Assert.that(valueField != null, "Field \'value\' of java.lang.String not found");
       }
     }
-    return charArrayToString((TypeArray) valueField.getValue(stringOop),
-                             offsetField.getValue(stringOop),
-                             countField.getValue(stringOop));
+    if (offsetField != null && countField != null) {
+      return charArrayToString((TypeArray) valueField.getValue(stringOop),
+                               offsetField.getValue(stringOop),
+                               countField.getValue(stringOop));
+    }
+    return  charArrayToString((TypeArray) valueField.getValue(stringOop));
   }
 
   public static String stringOopToEscapedString(Oop stringOop) {