Load the native call wrapper via Thread.

runtime/vm/assembler.h

Index: runtime/vm/assembler.h
diff --git a/runtime/vm/assembler.h b/runtime/vm/assembler.h
index bd3ca5b57dba1ef06b31a132ad7aec3799dee3fa..c414c0d56e740fea35f538ae8d46ccc468a2db37 100644
--- a/runtime/vm/assembler.h
+++ b/runtime/vm/assembler.h
@@ -290,14 +290,10 @@ class ObjectPoolWrapper : public ValueObject {
   intptr_t AddObject(const Object& obj,
                      Patchability patchable = kNotPatchable);
   intptr_t AddImmediate(uword imm);
-  intptr_t AddExternalLabel(const ExternalLabel* label,
-                            Patchability patchable);
 
   intptr_t FindObject(const Object& obj,
                       Patchability patchable = kNotPatchable);
   intptr_t FindImmediate(uword imm);
-  intptr_t FindExternalLabel(const ExternalLabel* label,
-                             Patchability patchable);
   intptr_t FindNativeEntry(const ExternalLabel* label,
                            Patchability patchable);