Remove well_known_types.Error and well_known_types.ParseError. (#449)

* Remove well_known_types.Error and well_known_types.ParseError.

* Add to CHANGELOG.

Author: songy23

contrib/opencensus-ext-ocagent/CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 
 ## Unreleased
+- Remove well_known_types.Error and well_known_types.ParseError.
+Note this could be a breaking change if you depend on an older 
+version of protobuf and use ParseError.
 
 ## 0.3.0
 Released 2019-04-24

contrib/opencensus-ext-ocagent/opencensus/ext/ocagent/utils/__init__.py

@@ -2,7 +2,6 @@
 import os
 import socket
 
-from google.protobuf.internal.well_known_types import ParseError
 from google.protobuf.timestamp_pb2 import Timestamp
 from opencensus.common.version import __version__ as opencensus_version
 from opencensus.proto.agent.common.v1 import common_pb2
@@ -59,6 +58,6 @@ def proto_ts_from_datetime_str(dt):
     if (dt is not None):
         try:
             ts.FromJsonString(dt)
-        except ParseError:
+        except ValueError:
             pass
     return ts