Introduce a class encapsulating arguments descriptor arrays.

runtime/vm/native_arguments.h

 // 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.
 
 #ifndef VM_NATIVE_ARGUMENTS_H_
 #define VM_NATIVE_ARGUMENTS_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/stub_code.h"
@@ skipping 32 matching lines @@
 
 
 // Class NativeArguments is used to access arguments passed in from
 // generated dart code to a runtime function or a dart library native
 // function. It is also used to set the return value if any at the slot
 // reserved for return values.
 // All runtime function/dart library native functions have the
 // following signature:
 //   void function_name(NativeArguments arguments);
 // Inside the function, arguments are accessed as follows:
-//   const Instance& arg0 = Instance::CheckedHandle(arguments.At(0));
-//   const Smi& arg1 = Smi::CheckedHandle(arguments.At(1));
+//   const Instance& arg0 = Instance::CheckedHandle(arguments.ArgAt(0));
+//   const Smi& arg1 = Smi::CheckedHandle(arguments.ArgAt(1));
 // The return value is set as follows:
 //   arguments.SetReturn(result);
 // NOTE: Since we pass 'this' as a pass-by-value argument in the stubs we don't
 // have DISALLOW_COPY_AND_ASSIGN in the class definition and do not make it a
 // subclass of ValueObject.
 class NativeArguments {
  public:
   Isolate* isolate() const { return isolate_; }
   int ArgCount() const { return ArgcBits::decode(argc_tag_); }
 
@@ skipping 96 matching lines @@
 
   Isolate* isolate_;  // Current isolate pointer.
   int argc_tag_;  // Encodes argument count and invoked native call type.
   RawObject*(*argv_)[];  // Pointer to an array of arguments to runtime call.
   RawObject** retval_;  // Pointer to the return value area.
 };
 
 }  // namespace dart
 
 #endif  // VM_NATIVE_ARGUMENTS_H_