Add panels as a single group of windows per display for overview window cycling.

ash/wm/overview/window_selector.h

Index: ash/wm/overview/window_selector.h
diff --git a/ash/wm/overview/window_selector.h b/ash/wm/overview/window_selector.h
index 4059540df807ca7de1fef563421c8d2a6f8e2167..b93b5dab1ec23cbca212e494331d7be8d57dc6dc 100644
--- a/ash/wm/overview/window_selector.h
+++ b/ash/wm/overview/window_selector.h
@@ -5,6 +5,7 @@
 #ifndef ASH_WM_OVERVIEW_WINDOW_SELECTOR_H_
 #define ASH_WM_OVERVIEW_WINDOW_SELECTOR_H_
 
+#include <set>
 #include <vector>
 
 #include "ash/ash_export.h"
@@ -31,7 +32,7 @@ class WindowSelectorTest;
 
 class WindowOverview;
 class WindowSelectorDelegate;
-class WindowSelectorWindow;
+class WindowSelectorItem;
 
 // The WindowSelector allows selecting a window by alt-tabbing (CYCLE mode) or
 // by clicking or tapping on it (OVERVIEW mode). A WindowOverview will be shown
@@ -94,9 +95,12 @@ class ASH_EXPORT WindowSelector
   // |focus|, restores focus to the stored window.
   void ResetFocusRestoreWindow(bool focus);
 
-  // The collection of windows in the overview wrapped by a helper class which
+  // The collection of items in the overview wrapped by a helper class which
   // restores their state and helps transform them to other root windows.
-  ScopedVector<WindowSelectorWindow> windows_;
+  ScopedVector<WindowSelectorItem> windows_;
+
+  // Tracks observed windows.
+  std::set<aura::Window*> observed_windows_;
 
   // The window selection mode.
   Mode mode_;