Ensure the previously active browser window gets the focus after a browser window is closed on OSX.

chrome/browser/ui/panels/panel_window_controller_cocoa.mm

Index: chrome/browser/ui/panels/panel_window_controller_cocoa.mm
diff --git a/chrome/browser/ui/panels/panel_window_controller_cocoa.mm b/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
index b4f0e6d263a61287cf050565300c00b929d1067f..215060aecc7f8b9cf55124978e2ce62b8939cd53 100644
--- a/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
+++ b/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
@@ -361,7 +361,9 @@ enum {
     return NO;
   }
 
-  // the tab strip is empty, it's ok to close the window
+  // The tab strip is empty, it's ok to close the window.
+  // Ensure focus goes to previous active browser window.
+  [BrowserWindowUtils selectPreviousActiveBrowserWindow:browser];
   return YES;
 }
 
@@ -609,5 +611,4 @@ enum {
   // cases when minimized Panel is getting keyboard input, invisibly.
   return windowShim_->panel()->expansion_state() == Panel::EXPANDED;
 }
-
 @end