Int64 accessor not supported by dart2js when using msgpack_dart

[asimfarooq5]

When using msgpack_dart with dart2js, I encountered an issue where Int64 accessor is not supported. This results in a JavaScript error when running the compiled code in a browser.

[YongTaiSin]

When using msgpack_dart with dart2js, I encountered an issue where Int64 accessor is not supported. This results in a JavaScript error when running the compiled code in a browser.

+1