Adds DebuggerPlugin CLI flags to parser.

def define_flags(self, parser):
    """Adds DebuggerPlugin CLI flags to parser."""
    group = parser.add_argument_group('debugger plugin')
    group.add_argument(
        '--debugger_data_server_grpc_port',
        metavar='PORT',
        type=int,
        default=-1,
        help='''\
The port at which the non-interactive debugger data server should
receive debugging data via gRPC from one or more debugger-enabled
TensorFlow runtimes. No debugger plugin or debugger data server will be
started if this flag is not provided. This flag differs from the
`--debugger_port` flag in that it starts a non-interactive mode. It is
for use with the "health pills" feature of the Graph Dashboard. This
flag is mutually exclusive with `--debugger_port`.\
''')
    group.add_argument(
        '--debugger_port',
        metavar='PORT',
        type=int,
        default=-1,
        help='''\
The port at which the interactive debugger data server (to be started by
the debugger plugin) should receive debugging data via gRPC from one or
more debugger-enabled TensorFlow runtimes. No debugger plugin or
debugger data server will be started if this flag is not provided. This
flag differs from the `--debugger_data_server_grpc_port` flag in that it
starts an interactive mode that allows user to pause at selected nodes
inside a TensorFlow Graph or between Session.runs. It is for use with
the interactive Debugger Dashboard. This flag is mutually exclusive with
`--debugger_data_server_grpc_port`.\
''')