message: refactor(animations): uses a loop instead Array.map() which creates and
  returns a new array that is discarded.
  This pattern will become a compilation error in google3.
  PR Close
diff: @@ -1225,7 +1225,7 @@ export class TransitionAnimationEngine {
  const targetTriggerName: string|undefined =
  instruction.isRemovalTransition ? undefined : triggerName;
  - instruction.timelines.map(timelineInstruction => {
  + for (const timelineInstruction of instruction.timelines) {
  const element = timelineInstruction.element;
  const isQueriedElement = element !== rootElement;
  const players = getOrSetAsInMap(allPreviousPlayersMap, element, []);
  @@ -1239,7 +1239,7 @@ export class TransitionAnimationEngine {
  player.destroy();
  players.push(player);
  });
  - });
  + }
  // this needs to be done so that the PRE/POST styles can be
  // computed properly without interfering with the previous animation
  