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

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/panels/panel_window_controller_cocoa.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/logging.h"
 #include "base/mac/bundle_locations.h"
@@ skipping 343 matching lines @@
     [self terminateBoundsAnimation];
     animateOnBoundsChange_ = NO;
     // Tab strip isn't empty. Make browser to close all the tabs, allowing the
     // renderer to shut down and call us back again.
     // The tab strip of Panel is not visible and contains only one tab but
     // it still has to be closed.
     browser->OnWindowClosing();
     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;
 }
 
 // When windowShouldClose returns YES (or if controller receives direct 'close'
 // signal), window will be unconditionally closed. Clean up.
 - (void)windowWillClose:(NSNotification*)notification {
   DCHECK(windowShim_->browser()->tabstrip_model()->empty());
   // Avoid callbacks from a nonblocking animation in progress, if any.
   [self terminateBoundsAnimation];
   windowShim_->DidCloseNativeWindow();
@@ skipping 227 matching lines @@
 }
 
 - (BOOL)canBecomeKeyWindow {
   // Panel can only gain focus if it is expanded. Minimized panels do not
   // participate in Cmd-~ rotation.
   // TODO(dimich): If it will be ever desired to expand/focus the Panel on
   // keyboard navigation or via main menu, the care should be taken to avoid
   // cases when minimized Panel is getting keyboard input, invisibly.
   return windowShim_->panel()->expansion_state() == Panel::EXPANDED;
 }
-
 @end