8359923: Const accessors for the Deferred class

Reviewed-by: jsjolen

Author: jsikstro

src/hotspot/share/utilities/deferred.hpp

@@ -56,14 +56,27 @@ class Deferred {
     return &_t;
   }
 
+  const T* get() const {
+    assert(_initialized, "must be initialized before access");
+    return &_t;
+  }
+
   T& operator*() {
     return *get();
   }
 
+  const T& operator*() const {
+    return *get();
+  }
+
   T* operator->() {
     return get();
   }
 
+  const T* operator->() const {
+    return get();
+  }
+
   template<typename... Ts>
   void initialize(Ts&... args) {
     assert(!_initialized, "Double initialization forbidden");