Undo "Don't include an object header for instructions in the text section."

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index ff32dcd23d28fd94cc38017fdd9245b019f17712..ca018822a22ff01357d910a8c5e881e16afd260c 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -1107,12 +1107,10 @@ class RawCode : public RawObject {
   uword entry_point_;
 
   RawObject** from() {
-    return reinterpret_cast<RawObject**>(&ptr()->instructions_);
+    return reinterpret_cast<RawObject**>(&ptr()->active_instructions_);
   }
-  union {
-    RawInstructions* instructions_;
-    RawSmi* precompiled_instructions_size_;
-  };
+  RawInstructions* active_instructions_;
+  RawInstructions* instructions_;
   RawObjectPool* object_pool_;
   // If owner_ is Function::null() the owner is a regular stub.
   // If owner_ is a Class the owner is the allocation stub for that class.