Release google-cloud-trace 0.34.1 (googleapis#2925)

* Fix bug (typo) in retrieving default on_error proc.

Release google-cloud-resource_manager 0.31.0 (googleapis#2915)

* Add parent resoure to `Project`:
  * Add `Project#parent`.
  * Add `parent` optional named argument to `Manager#create_project`.
  * Add `Resource` class.
  * Add `Manager#resource` convenience method.

Release google-cloud-pubsub 0.34.1 (googleapis#2924)

* Fix bug (typo) in retrieving default on_error proc.
* Update network configuration.

Release google-cloud-logging 1.6.2 (googleapis#2923)

* Fix bug (typo) in retrieving default on_error proc.

Release google-cloud-error_reporting 0.31.3 (googleapis#2922)

* Fix bug (typo) in retrieving default on_error proc.

Release google-cloud-debugger 0.33.3 (googleapis#2921)

* Fix bug (typo) in retrieving default on_error proc.

Release google-cloud-datastore 1.5.1 (googleapis#2926)

* Add ReadOnlyTransaction convenience methods:
  * Add ReadOnlyTransaction#query
  * Add ReadOnlyTransaction#gql
  * Add ReadOnlyTransaction#key

Release google-cloud-error_reporting 0.31.2 (googleapis#2909)

* Fix conversion code for ErrorEvent and Debugee.
  * Prepare for changes in JSON serialization coming in
    google-protobuf 3.7.

Release google-cloud-debugger 0.33.2 (googleapis#2905)

* Fix conversion code for ErrorEvent and Debugee.
  * Prepare for changes in JSON serialization coming in
    google-protobuf 3.7.

Release google-cloud-trace 0.34.0 (googleapis#2898)

* Add Trace on_error configuration.
* Middleware improvements:
  * Buffer traces and make batch API calls.
  * Back pressure is applied by limiting the number of queued API calls.
  * Errors will now be raised when there are not enough resources.
  * Errors are reported by calling the on_error callback.
* Make use of Credentials#project_id
  * Use Credentials#project_id
    If a project_id is not provided, use the value on the Credentials object.
    This value was added in googleauth 0.7.0.
  * Loosen googleauth dependency
    Allow for new releases up to 0.10.
    The googleauth devs have committed to maintaining the current API
    and will not make backwards compatible changes before 0.10.
* Update Trace documentation
  * Correct the C-code's comments.