fix structured-cloning with getter properties

Getter property would not be copied during structured-cloning, no Error
is mentioned in the spec (infrastructure.html#structured-clone). The
original case contained 2 independent cases, which can be separated.
getter_cloning_should_propagate_exceptions

Agree with the reviewer's comment. Follow the steps defined in 8.2.
Remove unnecessary whitespace

Remove unnecessary whitespace
Merge pull request #1438 from siusin/fix-webmessaging-withoutports026-getterclone

fix structured-cloning with getter properties