Rework leaf calls as just simple C calls with a signature and not the NativeArgumentDescriptor.

vm/code_generator.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/code_generator.h"
 
 #include "vm/assembler_macros.h"
 #include "vm/code_patcher.h"
 #include "vm/compiler.h"
 #include "vm/dart_api_impl.h"
@@ skipping 1566 matching lines @@
     }
   }
   // The cache is null terminated, therefore the loop above should never
   // terminate by itself.
   UNREACHABLE();
   return Code::null();
 }
 
 
 // Adds a pointer to the store buffer.
-// Arg0: the address of a field being stored into
-DEFINE_LEAF_RUNTIME_ENTRY(StoreBuffer, 1) {
-  ASSERT(args.Count() == kStoreBufferRuntimeEntry.argument_count());
-  uword ptr = reinterpret_cast<uword>(args.At(0));
-  isolate->store_buffer()->AddPointer(ptr);
-  return Smi::New(0);  // Just an arbitrary RawObject* value.
+// ptr: the address of a field being stored into.
+DEFINE_LEAF_RUNTIME_ENTRY(void, StoreBuffer, uword ptr) {
+  Isolate::Current()->store_buffer()->AddPointer(ptr);
 }
+END_LEAF_RUNTIME_ENTRY
 
 }  // namespace dart