Make Page Visibility API work when the browser window is visible or not

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
index 784446e2dfced277d11e5800b29d1bcada28ee1b..1e8b01c58d52d8c4d3fe6238a8b526b2bb4b3ea5 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
@@ -1715,6 +1715,14 @@ uint32_t DesktopWindowTreeHostX11::DispatchEvent(
       }
       break;
     }
+    case VisibilityNotify:
+      // Allows to trigger visibilityChange events when the browser window
+      // is minimized or restored.
+      if (xev->xvisibility.state == VisibilityFullyObscured)
+         content_window_->SetPageVisibility(false);
+      else
+         content_window_->SetPageVisibility(true);
+      break;
     case FocusOut:
       if (xev->xfocus.mode != NotifyGrab) {
         ReleaseCapture();
@@ -1747,8 +1755,20 @@ uint32_t DesktopWindowTreeHostX11::DispatchEvent(
       previous_bounds_ = bounds_;
       bounds_ = bounds;
 
-      if (origin_changed)
+      if (origin_changed) {
         OnHostMoved(bounds_.origin());
+        // Allows to trigger visibilityChange events while swithcing between
+        // workspaces.
+        ::Screen* screen = DefaultScreenOfDisplay(xdisplay_);
+        int screen_width = WidthOfScreen(screen);
+        int screen_height = HeightOfScreen(screen);
+
+        if (translated_x < 0 || translated_x > screen_width ||
+            translated_y < 0 || translated_y > screen_height)
+          content_window_->SetPageVisibility(false);
+        else
+          content_window_->SetPageVisibility(true);
+      }
 
       if (size_changed) {
         delayed_resize_task_.Reset(base::Bind(