code: public Observable<WorkflowTriggerHistoryInner> getAsync(String resourceGroupName, String workflowName, String triggerName, String historyName) {
          return getWithServiceResponseAsync(resourceGroupName, workflowName, triggerName, historyName).map(new Func1<ServiceResponse<WorkflowTriggerHistoryInner>, WorkflowTriggerHistoryInner>() {
              @Override
              public WorkflowTriggerHistoryInner call(ServiceResponse<WorkflowTriggerHistoryInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets a workflow trigger history.
  
  @param resourceGroupName The resource group name.
  @param workflowName The workflow name.
  @param triggerName The workflow trigger name.
  @param historyName The workflow trigger history name. Corresponds to the run name for triggers that resulted in a run.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the WorkflowTriggerHistoryInner object