Defer preparing for overview until all overview items are initialized.

ash/wm/overview/window_selector.cc

Index: ash/wm/overview/window_selector.cc
diff --git a/ash/wm/overview/window_selector.cc b/ash/wm/overview/window_selector.cc
index 467aca6a8be669310006d0cafc85b779f1f87e3f..4c3930c1d767cb0062f266572d60b23886cbdd9e 100644
--- a/ash/wm/overview/window_selector.cc
+++ b/ash/wm/overview/window_selector.cc
@@ -124,6 +124,15 @@ WindowSelector::WindowSelector(const WindowList& windows,
     grid_list_.push_back(grid.release());
   }
 
+  // Do not call PrepareForOverview until all items are added to window_list_ as
+  // we don't want to cause any window updates until all windows in overview
+  // are observed. See http://crbug.com/384495.
+  for (ScopedVector<WindowGrid>::iterator iter = grid_list_.begin();
+       iter != grid_list_.end(); ++iter) {
+    (*iter)->PrepareForOverview();
+    (*iter)->PositionWindows(true);
+  }
+
   DCHECK(!grid_list_.empty());
   UMA_HISTOGRAM_COUNTS_100("Ash.WindowSelector.Items", num_items_);