Improve the quality of ARC notification snapshot

Previously it was rarely visible but now it's visible on closing. So
this CL improves the quality of shapshot by enabling shrink filter.

Bug: none
Change-Id: Ic509de0d83d5641f9a18acdb73e759639cb38507
Reviewed-on: https://chromium-review.googlesource.com/c/1255749Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Commit-Queue: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596113}

ash/system/message_center/arc/arc_notification_content_view.cc

@@ -683,7 +683,7 @@ void ArcNotificationContentView::OnPaint(gfx::Canvas* canvas) {
     canvas->DrawImageInt(
         item_->GetSnapshot(), 0, 0, item_->GetSnapshot().width(),
         item_->GetSnapshot().height(), contents_bounds.x(), contents_bounds.y(),
-        contents_bounds.width(), contents_bounds.height(), false);
+        contents_bounds.width(), contents_bounds.height(), true /* filter */);
   } else {
     // Draw a blank background otherwise. The height of the view and surface are
     // not exactly synced and user may see the blank area out of the surface.