Pubsub: Add custom docstrings for FlowControl enum and values (via synth).

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/pubsub/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:6ced5a36b08b82a328c69844e629300d58c14067f25cadab47f52542bdef7daf
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/pubsub/artman_pubsub.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/pubsub-v1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/pubsub/v1/pubsub.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/pubsub-v1/google/cloud/pubsub_v1/proto/pubsub.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/pubsub-v1/google/cloud/pubsub_v1/proto.
synthtool > Replaced 'from google.cloud import pubsub_v1' in tests/unit/gapic/v1/test_publisher_client_v1.py.
synthtool > Replaced ' pubsub_v1' in tests/unit/gapic/v1/test_publisher_client_v1.py.
synthtool > Replaced 'from google.cloud import pubsub_v1' in tests/unit/gapic/v1/test_subscriber_client_v1.py.
synthtool > Replaced ' pubsub_v1' in tests/unit/gapic/v1/test_subscriber_client_v1.py.
synthtool > Replaced '# The name of the interface for this client. This is the key used to' in google/cloud/pubsub_v1/gapic/publisher_client.py.
synthtool > Replaced '# The name of the interface for this client. This is the key used to' in google/cloud/pubsub_v1/gapic/subscriber_client.py.
synthtool > Replaced 'import google.api_core.gapic_v1.method\n' in google/cloud/pubsub_v1/gapic/publisher_client.py.
synthtool > Replaced 'DESCRIPTOR = _MESSAGESTORAGEPOLICY,\n\\s+__module__.*\n\\s+,\n\\s+__doc__ = """' in google/cloud/pubsub_v1/proto/pubsub_pb2.py.
synthtool > No replacements made in google/cloud/pubsub_v1/gapic/subscriber_client.py for pattern subscription \(str\): The subscription whose backlog .*
(.*
)+?\s+Format is .*, maybe replacement is not longer needed?
synthtool > Replaced 'import functools\n' in google/cloud/pubsub_v1/gapic/publisher_client.py.
synthtool > Replaced 'import pkg_resources\n' in google/cloud/pubsub_v1/gapic/publisher_client.py.
synthtool > Replaced 'class PublisherClient' in google/cloud/pubsub_v1/gapic/publisher_client.py.
synthtool > Replaced 'client_config \\(dict\\): DEPRECATED.' in google/cloud/pubsub_v1/gapic/publisher_client.py.
synthtool > Replaced '# Raise deprecation warnings .*\n.*\n.*\n.*\n.*\n.*\n' in google/cloud/pubsub_v1/gapic/publisher_client.py.
synthtool > Replaced 'FlowControl.__new__.__defaults__ = \\(.*?\\)' in google/cloud/pubsub_v1/types.py.
.coveragerc
.flake8
MANIFEST.in
noxfile.py.j2
setup.cfg
Running session blacken
Creating virtualenv using python3.6 in .nox/blacken
pip install black
black docs google tests noxfile.py setup.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub_v1/gapic/subscriber_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub_v1/gapic/publisher_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub_v1/gapic/transports/publisher_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub_v1/gapic/transports/subscriber_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub_v1/gapic/publisher_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub_v1/proto/pubsub_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/tests/system/gapic/v1/test_system_publisher_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub_v1/gapic/subscriber_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/noxfile.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/tests/unit/gapic/v1/test_publisher_client_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/tests/unit/gapic/v1/test_subscriber_client_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/pubsub/google/cloud/pubsub_v1/proto/pubsub_pb2.py
All done! ✨ 🍰 ✨
15 files reformatted, 49 files left unchanged.
Session blacken was successful.
synthtool > Cleaned up 3 temporary directories.
synthtool > Wrote metadata to synth.metadata.