message: reflow: call interaction.start
diff: @@ -124,9 +124,8 @@ function startReflow (scope, interactable, element, action, event) {
  })
  : null;
  - signalArg.phase = 'start';
  interaction._reflowPromise = reflowPromise;
  - interaction._interacting = interaction._doPhase(signalArg);
  + interaction.start(action, interactable, element);
  if (interaction._interacting) {
  interaction.move(signalArg);
  