Defer preparing for overview until all overview items are initialized.

ash/wm/overview/window_grid.h

Index: ash/wm/overview/window_grid.h
diff --git a/ash/wm/overview/window_grid.h b/ash/wm/overview/window_grid.h
index fe4bf780ccc21a98c4ef46edd122fd684f5a437c..28af47c9ee4f71236dc9cd79f14a791c5dbdbe1b 100644
--- a/ash/wm/overview/window_grid.h
+++ b/ash/wm/overview/window_grid.h
@@ -51,6 +51,10 @@ class ASH_EXPORT WindowGrid : public aura::WindowObserver {
              WindowSelector* window_selector);
   virtual ~WindowGrid();
 
+  // Prepares the windows in this grid for overview. This will restore all
+  // minimized windows and ensure they are visible.
+  void PrepareForOverview();
+
   // Positions all the windows in the grid.
   void PositionWindows(bool animate);