Defer preparing for overview until all overview items are initialized.

ash/wm/overview/window_grid.cc

Index: ash/wm/overview/window_grid.cc
diff --git a/ash/wm/overview/window_grid.cc b/ash/wm/overview/window_grid.cc
index 99ea37c2d1e54056e20674b2f1366eb468a595f8..8275c97e295422ded9cef1a175f0935dbf4a4148 100644
--- a/ash/wm/overview/window_grid.cc
+++ b/ash/wm/overview/window_grid.cc
@@ -136,7 +136,6 @@ WindowGrid::WindowGrid(aura::Window* root_window,
       continue;
     (*iter)->AddObserver(this);
     observed_windows_.insert(*iter);
-    WindowSelectorItem* item = NULL;
 
     if ((*iter)->type() == ui::wm::WINDOW_TYPE_PANEL &&
         wm::GetWindowState(*iter)->panel_attached()) {
@@ -147,20 +146,12 @@ WindowGrid::WindowGrid(aura::Window* root_window,
         window_list_.push_back(panels_item);
       }
       panels_item->AddWindow(*iter);
-      item = panels_item;
     } else {
-      item = new WindowSelectorWindow(*iter);
-      item->PrepareForOverview();
-      window_list_.push_back(item);
+      window_list_.push_back(new WindowSelectorWindow(*iter));
     }
   }
   if (window_list_.empty())
     return;
-
-  if (panels_item)
-    panels_item->PrepareForOverview();
-
-  PositionWindows(true);
 }
 
 WindowGrid::~WindowGrid() {
@@ -170,6 +161,13 @@ WindowGrid::~WindowGrid() {
   }
 }
 
+void WindowGrid::PrepareForOverview() {
+  for (ScopedVector<WindowSelectorItem>::iterator iter = window_list_.begin();
+       iter != window_list_.end(); ++iter) {
+    (*iter)->PrepareForOverview();
+  }
+}
+
 void WindowGrid::PositionWindows(bool animate) {
   CHECK(!window_list_.empty());