Load the native call wrapper via Thread.

runtime/vm/assembler_arm64.h

 // Copyright (c) 2014, 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_ARM64_H_
 #define VM_ASSEMBLER_ARM64_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_arm64.h directly; use assembler.h instead.
 #endif
@@ skipping 1267 matching lines @@
 
   bool constant_pool_allowed() const {
     return constant_pool_allowed_;
   }
   void set_constant_pool_allowed(bool b) {
     constant_pool_allowed_ = b;
   }
 
   intptr_t FindImmediate(int64_t imm);
   bool CanLoadFromObjectPool(const Object& object) const;
-  void LoadExternalLabel(Register dst, const ExternalLabel* label);
   void LoadNativeEntry(Register dst, const ExternalLabel* label);
-  void LoadExternalLabelFixed(Register dst,
-                              const ExternalLabel* label,
-                              Patchability patchable);
   void LoadFunctionFromCalleePool(Register dst,
                                   const Function& function,
                                   Register new_pp);
   void LoadIsolate(Register dst);
   void LoadObject(Register dst, const Object& obj);
   void LoadUniqueObject(Register dst, const Object& obj);
   void LoadDecodableImmediate(Register reg, int64_t imm);
   void LoadImmediateFixed(Register reg, int64_t imm);
   void LoadImmediate(Register reg, int64_t imm);
   void LoadDImmediate(VRegister reg, double immd);
@@ skipping 621 matching lines @@
                                   Register value,
                                   Label* no_update);
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_ARM64_H_