'Adds a \'postbuild\' variable if there is a postbuild for |output|.'

def AppendPostbuildVariable(self, variables, spec, output, binary, is_command_start=False):

    postbuild = self.GetPostbuildCommand(spec, output, binary, is_command_start)
    if postbuild:
        variables.append(('postbuilds', postbuild))
