(Experimental) Add Brooks pointers (libcore).

This feature is disabled by default.

Change-Id: Ia8db311c1bc994737964121700a70b33920ddc4a
diff --git a/libart/src/main/java/java/lang/Object.java b/libart/src/main/java/java/lang/Object.java
index 81e3872..ed2f153 100644
--- a/libart/src/main/java/java/lang/Object.java
+++ b/libart/src/main/java/java/lang/Object.java
@@ -133,6 +133,15 @@
     private transient Class<?> shadow$_klass_;
     private transient int shadow$_monitor_;
 
+    // Uncomment the following two fields to enable brooks pointers.
+    // Meant to do "#ifdef USE_BROOKS_POINTER ... #endif" but no macros.
+    //
+    // Note names use a 'x' prefix and the _x_brooks_ptr_ field is of
+    // type int instead of Object to go with the alphabetical/by-type
+    // field order.
+    // private transient int shadow$_x_brooks_ptr_;
+    // private transient int shadow$_x_padding_;
+
     /**
      * Constructs a new instance of {@code Object}.
      */