Avoid overwriting '__module__' of messages from shared modules. (#5364)

Note that we *are* still overwriting it for messages from modules defined
within the current package.

See #4715.

packages/google-cloud-texttospeech/google/cloud/texttospeech_v1beta1/types.py

@@ -15,18 +15,30 @@
 from __future__ import absolute_import
 import sys
 
-from google.api_core.protobuf_helpers import get_messages
-
 from google.api import http_pb2
-from google.cloud.texttospeech_v1beta1.proto import cloud_tts_pb2
 from google.protobuf import descriptor_pb2
 
+from google.api_core.protobuf_helpers import get_messages
+from google.cloud.texttospeech_v1beta1.proto import cloud_tts_pb2
+
+
+_shared_modules = [
+    http_pb2,
+    descriptor_pb2,
+]
+
+_local_modules = [
+    cloud_tts_pb2,
+]
+
 names = []
-for module in (
-        http_pb2,
-        cloud_tts_pb2,
-        descriptor_pb2,
-):
+
+for module in _shared_modules:
+    for name, message in get_messages(module).items():
+        setattr(sys.modules[__name__], name, message)
+        names.append(name)
+
+for module in _local_modules:
     for name, message in get_messages(module).items():
         message.__module__ = 'google.cloud.texttospeech_v1beta1.types'
         setattr(sys.modules[__name__], name, message)