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

ui/aura/window.h

Index: ui/aura/window.h
diff --git a/ui/aura/window.h b/ui/aura/window.h
index d6d6f7a574a84c4d4be8c62f1174932091ae259b..4ff12b3e3e2705c4ac1ddb2e528f648670bc2223 100644
--- a/ui/aura/window.h
+++ b/ui/aura/window.h
@@ -136,6 +136,9 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
   // Changes the visibility of the window.
   void Show();
   void Hide();
+#if defined(OS_LINUX)
+  void SetPageVisibility(bool visibility);
+#endif
   // Returns true if this window and all its ancestors are visible.
   bool IsVisible() const;
   // Returns the visibility requested by this window. IsVisible() takes into
@@ -442,15 +445,19 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
 
   // Methods implementing visibility change notifications. See WindowObserver
   // for more details.
-  void NotifyWindowVisibilityChanged(aura::Window* target, bool visible);
+  void NotifyWindowVisibilityChanged(aura::Window* target, bool visible,
+                                     bool content_visible);
   // Notifies this window's observers. Returns false if |this| was deleted
   // during the call (by an observer), otherwise true.
   bool NotifyWindowVisibilityChangedAtReceiver(aura::Window* target,
-                                               bool visible);
+                                               bool visible,
+                                               bool content_visible);
   // Notifies this window and its child hierarchy. Returns false if
   // |this| was deleted during the call (by an observer), otherwise
   // true.
-  bool NotifyWindowVisibilityChangedDown(aura::Window* target, bool visible);
+  bool NotifyWindowVisibilityChangedDown(aura::Window* target,
+                                         bool visible,
+                                       bool content_visible);
   // Notifies this window and its parent hierarchy.
   void NotifyWindowVisibilityChangedUp(aura::Window* target, bool visible);