Alter the native code generator to directly use  Dart_SetBooleanReturnValue  Dart_SetIntReturnValue  Dart_SetDoubleReturnValue
Alter the native code generator to directly use
 Dart_SetBooleanReturnValue
 Dart_SetIntReturnValue
 Dart_SetDoubleReturnValue

instead of 
 Dart_Handle retval = toDart(...); // Calls Dart_Boolean, Dart_NewInteger,
                                   // Dart_Double.
 Dart_SetReturnValue(args, retval);

R=vsm@google.com

Review URL: https://codereview.chromium.org//21156011

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@25698 260f80e4-7a28-3924-810f-c04153c831b5

dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk