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

vm/assembler_x64.cc

 // Copyright (c) 2011, 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/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/heap.h"
 #include "vm/memory_region.h"
@@ skipping 1461 matching lines @@
   }
 }
 
 
 void Assembler::LeaveFrame() {
   movq(RSP, RBP);
   popq(RBP);
 }
 
 
+void Assembler::ReserveAlignedFrameSpace(intptr_t frame_space) {
+  // Reserve space for arguments and align frame before entering
+  // the C++ world.
+  AddImmediate(RSP, Immediate(-frame_space));
+  if (OS::ActivationFrameAlignment() > 0) {
+    andq(RSP, Immediate(~(OS::ActivationFrameAlignment() - 1)));
+  }
+}
+
+
 void Assembler::CallRuntime(const RuntimeEntry& entry) {
   entry.Call(this);
 }
 
 
 void Assembler::Align(int alignment, int offset) {
   ASSERT(Utils::IsPowerOfTwo(alignment));
   int pos = offset + buffer_.GetPosition();
   int mod = pos & (alignment - 1);
   if (mod == 0) {
@@ skipping 182 matching lines @@
     comments.SetCommentAt(i, comments_[i]->comment());
   }
 
   return comments;
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64