Make subtype test stubs isolate-specific.

runtime/vm/assembler_x64.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ASSEMBLER_X64_H_
 #define VM_ASSEMBLER_X64_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_x64.h directly; use assembler.h instead.
 #endif
@@ skipping 736 matching lines @@
   // Call runtime function. Reserves shadow space on the stack before calling
   // if platform ABI requires that. Does not restore RSP after the call itself.
   void CallCFunction(const ExternalLabel* label);
   void CallCFunction(Register reg);
 
   /*
    * Loading and comparing classes of objects.
    */
   void LoadClassId(Register result, Register object);
 
-  void LoadClassById(Register result, Register class_id);
+  void LoadClassById(Register result,
+                     Register class_id,
+                     Isolate* isolate,
+                     Register pp);
 
-  void LoadClass(Register result, Register object);
+  void LoadClass(Register result,
+                 Register object,
+                 Isolate* isolate,
+                 Register pp);
 
   void CompareClassId(Register object, intptr_t class_id);
 
   void LoadTaggedClassIdMayBeSmi(Register result, Register object);
 
   // CheckClassIs fused with optimistic SmiUntag.
   // Value in the register object is untagged optimistically.
   void SmiUntagOrCheckClass(Register object, intptr_t class_id, Label* smi);
 
   /*
@@ skipping 358 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_X64_H_