Make Picture-in-Picture window visible on all workspaces.

This CL makes sure Picture-in-Picture window is always visible on all
workspaces by calling SetVisibleOnAllWorkspaces when it is shown.

Bug: 954470
Change-Id: If1f60781dd79cb8fb884cb41f3fe596e77fd9438
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575598
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652736}

chrome/browser/ui/views/overlay/overlay_window_views.cc

@@ -562,6 +562,7 @@ void OverlayWindowViews::Close() {
 
 void OverlayWindowViews::ShowInactive() {
   views::Widget::ShowInactive();
+  views::Widget::SetVisibleOnAllWorkspaces(true);
 #if defined(OS_CHROMEOS)
   // For rounded corners.
   if (ash::features::IsPipRoundedCornersEnabled()) {