It seems save and correct to remove that field.

diff -r e554994dd16a src/share/classes/java/lang/ClassValue.java
--- a/src/share/classes/java/lang/ClassValue.java Fri Dec 13 09:36:06 2013 -0800
+++ b/src/share/classes/java/lang/ClassValue.java Thu Jan 23 13:00:37 2014 -0800
@@ -375,10 +375,10 @@ public abstract class ClassValue<T> {
         synchronized (CRITICAL_SECTION) { // private object to avoid deadlocks
             // happens about once per type
             if ((map = type.classValueMap) == null)
- type.classValueMap = map = new ClassValueMap(type);
+ type.classValueMap = map = new ClassValueMap();
         }
- return map;
- }
+ return map;
+ }
 
     static <T> Entry<T> makeEntry(Version<T> explicitVersion, T value) {
         // Note that explicitVersion might be different from this.version.
@@ -398,12 +398,11 @@ public abstract class ClassValue<T> {
 
     // The following class could also be top level and non-public:
 
- /** A backing map for all ClassValues, relative a single given type.
+ /** A backing map for all ClassValues.
      * Gives a fully serialized "true state" for each pair (ClassValue cv, Class type).
      * Also manages an unserialized fast-path cache.
      */
     static class ClassValueMap extends WeakHashMap<ClassValue.Identity, Entry<?>> {
- private final Class<?> type;
         private Entry<?>[] cacheArray;
         private int cacheLoad, cacheLoadLimit;
 
@@ -413,11 +412,10 @@ public abstract class ClassValue<T> {
          */
         private static final int INITIAL_ENTRIES = 32;
 
- /** Build a backing map for ClassValues, relative the given type.
+ /** Build a backing map for ClassValues.
          * Also, create an empty cache array and install it on the class.
          */
- ClassValueMap(Class<?> type) {
- this.type = type;
+ ClassValueMap() {
             sizeCache(INITIAL_ENTRIES);
         }