message: [popover] got rid of flickering when mdl-select drop-down do not have enough space available at the bottom
diff: @@ -170,19 +170,14 @@ export class MdlPopoverComponent {
  private updateDirection(event: Event, forElement: any = null) {
  const popoverElement = this.elementRef.nativeElement;
  - const positionUpdateRequired = forElement && this.position;
  - if (positionUpdateRequired) {
  popoverElement.style.visibility = 'hidden';
  - }
  setTimeout(() => {
  - if (positionUpdateRequired) {
  + if (forElement && this.position) {
  const forHtmlElement = this.getHtmlElement(forElement);
  this.popupPositionService.updatePosition(forHtmlElement, popoverElement, this.position);
  popoverElement.style.visibility = 'visible';
  this.changeDetectionRef.markForCheck();
  - // since we have user specified directions maybe it's better to let user to decide when and where the popup should be directed at?
  - // my point: we should not use the following code with "auto dirrection up"
  return;
  }
  @@ -192,6 +187,7 @@ export class MdlPopoverComponent {
  if (height) {
  const bottomSpaceAvailable = viewHeight - targetRect.bottom
  this.directionUp = bottomSpaceAvailable < height;
  + popoverElement.style.visibility = 'visible';
  this.changeDetectionRef.markForCheck();
  }
  });
  