Fixed volume slider element event handling

MediaControlVolumeSliderElement::defaultEventHandler has making
redundant calls to setVolume() & setMuted() on mouse activity. E.g. if
a mouse click changed the slider position, the above calls were made 4
times, once for each of these events: mousedown, input, mouseup,
DOMActive, click. This crack got exposed when PointerEvents are enabled
by default on M55, adding pointermove, pointerdown & pointerup to the
list.

This CL fixes the code to trigger the calls to setVolume() & setMuted()
only when the slider position is changed. Also added pointer events to
certain lists of mouse events in the code.

BUG=677900

Review-Url: https://codereview.chromium.org/2622273003
Cr-Commit-Position: refs/heads/master@{#446032}
 void MediaControlVolumeSliderElement::defaultEventHandler(Event* event) {
   if (!isConnected() || !document().isActive())
     return;
 
   MediaControlInputElement::defaultEventHandler(event);
 
   if (event->type() == EventTypeNames::mousedown)
     Platform::current()->recordAction(
         UserMetricsAction("Media.Controls.VolumeChangeBegin"));

  if (event->type() == EventTypeNames::mouseup)
     Platform::current()->recordAction(
         UserMetricsAction("Media.Controls.VolumeChangeEnd"));
 
  if (event->type() == EventTypeNames::input) {
    double volume = value().toDouble();
    mediaElement().setVolume(volume);
    mediaElement().setMuted(false);
  }
 }

 void MediaControlVolumeSliderElement::defaultEventHandler(Event* event) {
  if (event->isMouseEvent() &&
      toMouseEvent(event)->button() !=
          static_cast<short>(WebPointerProperties::Button::Left))
    return;
   if (!isConnected() || !document().isActive())
     return;
 
   MediaControlInputElement::defaultEventHandler(event);
 
  if (event->type() == EventTypeNames::mouseover ||
      event->type() == EventTypeNames::mouseout ||
      event->type() == EventTypeNames::mousemove)
    return;
   if (event->type() == EventTypeNames::mousedown)
     Platform::current()->recordAction(
         UserMetricsAction("Media.Controls.VolumeChangeBegin"));

  if (event->type() == EventTypeNames::mouseup)
     Platform::current()->recordAction(
         UserMetricsAction("Media.Controls.VolumeChangeEnd"));
 
  double volume = value().toDouble();
  mediaElement().setVolume(volume);
  mediaElement().setMuted(false);
 }
