OMX: add event for rendering an output frame by a tunneled decoder

Bug: 20503131
Change-Id: Ia5cc7629244c986f059a3571be1d8aca87006e02
diff --git a/include/media/openmax/OMX_AsString.h b/include/media/openmax/OMX_AsString.h
index 7856c06..65eb562 100644
--- a/include/media/openmax/OMX_AsString.h
+++ b/include/media/openmax/OMX_AsString.h
@@ -287,6 +287,7 @@
 //      case OMX_EventComponentResumed:          return "ComponentResumed";
 //      case OMX_EventDynamicResourcesAvailable: return "DynamicResourcesAvailable";
 //      case OMX_EventPortFormatDetected:        return "PortFormatDetected";
+        case OMX_EventOutputRendered:            return "OutputRendered";
         default:                                 return def;
     }
 }