MigrationProgressEvent

 { 
 "step" 
 : 
 enum (  MigrationStep 
 
) 
 , 
 // Union field step_details 
can be only one of the following: 
 "prepareStepDetails" 
 : 
 { 
 object (  PrepareStepDetails 
 
) 
 } 
 , 
 "redirectWritesStepDetails" 
 : 
 { 
 object (  RedirectWritesStepDetails 
 
) 
 } 
 // End of list of possible types for union field step_details 
. 
 }