Revert "Remove Code::active_instructions_."

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 23163fb3f136c1c7dd9ac9e77a098407e2a3456e..4271a58f28d9962cb82ce48ebf1145cc89adfd1b 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -4324,7 +4324,9 @@ class DeoptInfo : public AllStatic {
 
 class Code : public Object {
  public:
-  uword active_entry_point() const { return raw_ptr()->entry_point_; }
+  RawInstructions* active_instructions() const {
+    return raw_ptr()->active_instructions_;
+  }
 
   RawInstructions* instructions() const { return raw_ptr()->instructions_; }
 
@@ -4606,11 +4608,12 @@ class Code : public Object {
   void Enable() const {
     if (!IsDisabled()) return;
     ASSERT(Thread::Current()->IsMutatorThread());
+    ASSERT(instructions() != active_instructions());
     SetActiveInstructions(instructions());
   }
 
   bool IsDisabled() const {
-    return active_entry_point() != EntryPoint();
+    return instructions() != active_instructions();
   }
 
  private: