Web Risk: Make threat_types a required argument to search_hashes (via synth).

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/webrisk/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:0e6f3a668cd68afc768ecbe08817cf6e56a0e64fcbdb1c58c3b97492d12418a1
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/webrisk/artman_webrisk_v1beta1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/webrisk-v1beta1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/cloud/webrisk/v1beta1/webrisk.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/webrisk-v1beta1/google/cloud/webrisk_v1beta1/proto/webrisk.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/webrisk-v1beta1/google/cloud/webrisk_v1beta1/proto.
synthtool > Replaced '__doc__ = """Attributes:' in google/cloud/webrisk_v1beta1/proto/webrisk_pb2.py.
.coveragerc
.flake8
MANIFEST.in
noxfile.py.j2
setup.cfg
Running session blacken
Creating virtual environment (virtualenv) using python3.6 in .nox/blacken
pip install black
black google tests docs
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk_v1beta1/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk_v1beta1/gapic/enums.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk_v1beta1/gapic/web_risk_service_v1_beta1_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk_v1beta1/gapic/transports/web_risk_service_v1_beta1_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/docs/conf.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk_v1beta1/types.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk_v1beta1/proto/webrisk_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk_v1beta1/gapic/web_risk_service_v1_beta1_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/tests/unit/gapic/v1beta1/test_web_risk_service_v1_beta1_client_v1beta1.py
reformatted /tmpfs/src/git/autosynth/working_repo/webrisk/google/cloud/webrisk_v1beta1/proto/webrisk_pb2.py
All done! ✨ 🍰 ✨
13 files reformatted, 3 files left unchanged.
Session blacken was successful.
synthtool > Cleaned up 2 temporary directories.
synthtool > Wrote metadata to synth.metadata.