Revert "Revert "Revert "Add intrinsic for Reference.get()"""

This reverts commit d4415e8bd04c4a9367744ff0149597b4f37a0e0a.

Change-Id: I34553ccbdcfea35c7742d21be2a74dc7085ab2a0
diff --git a/runtime/gc/reference_processor.h b/runtime/gc/reference_processor.h
index 91328a3..2771ea8 100644
--- a/runtime/gc/reference_processor.h
+++ b/runtime/gc/reference_processor.h
@@ -30,7 +30,6 @@
 namespace mirror {
 class Object;
 class Reference;
-class ReferenceClass;
 }  // namespace mirror
 
 namespace gc {
@@ -50,7 +49,6 @@
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
       LOCKS_EXCLUDED(lock_);
-  // The slow path bool is contained in the reference class object, can only be set once
   // Only allow setting this with mutators suspended so that we can avoid using a lock in the
   // GetReferent fast path as an optimization.
   void EnableSlowPath() EXCLUSIVE_LOCKS_REQUIRED(Locks::mutator_lock_);
@@ -62,7 +60,7 @@
                               IsHeapReferenceMarkedCallback* is_marked_callback, void* arg)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   void UpdateRoots(IsMarkedCallback* callback, void* arg)
-      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_, Locks::heap_bitmap_lock_);
+    SHARED_LOCKS_REQUIRED(Locks::mutator_lock_, Locks::heap_bitmap_lock_);
 
  private:
   class ProcessReferencesArgs {
@@ -77,10 +75,8 @@
     MarkObjectCallback* mark_callback_;
     void* arg_;
   };
-  bool SlowPathEnabled() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
   // Called by ProcessReferences.
-  void DisableSlowPath(Thread* self) EXCLUSIVE_LOCKS_REQUIRED(lock_)
-      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void DisableSlowPath(Thread* self) EXCLUSIVE_LOCKS_REQUIRED(lock_);
   // If we are preserving references it means that some dead objects may become live, we use start
   // and stop preserving to block mutators using GetReferrent from getting access to these
   // referents.
@@ -88,6 +84,8 @@
   void StopPreservingReferences(Thread* self) LOCKS_EXCLUDED(lock_);
   // Process args, used by the GetReferent to return referents which are already marked.
   ProcessReferencesArgs process_references_args_ GUARDED_BY(lock_);
+  // Boolean for whether or not we need to go slow path in GetReferent.
+  volatile bool slow_path_enabled_;
   // Boolean for whether or not we are preserving references (either soft references or finalizers).
   // If this is true, then we cannot return a referent (see comment in GetReferent).
   bool preserving_references_ GUARDED_BY(lock_);