Mac Panels changed to hide tab contents view after tab contents are gone.

chrome/browser/ui/panels/panel_window_controller_cocoa.mm

 // Copyright (c) 2011 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/mac_util.h"
@@ skipping 231 matching lines @@
   NSView* contentView = [[self window] contentView];
   [contentView addSubview:[findBarCocoaController view]];
 
   CGFloat maxY = NSMaxY([contentView frame]);
   CGFloat maxWidth = NSWidth([contentView frame]);
   [findBarCocoaController positionFindBarViewAtMaxY:maxY maxWidth:maxWidth];
 }
 
 - (void)tabInserted:(TabContents*)contents {
   [contentsController_ changeTabContents:contents];
+  DCHECK(![[contentsController_ view] isHidden]);
 }
 
 - (void)tabDetached:(TabContents*)contents {
   DCHECK(contents == [contentsController_ tabContents]);
   [contentsController_ changeTabContents:NULL];
+  [[contentsController_ view] setHidden:YES];
 }
 
 - (PanelTitlebarViewCocoa*)titlebarView {
   return titlebar_view_;
 }
 
 // Called to validate menu and toolbar items when this window is key. All the
 // items we care about have been set with the |-commandDispatch:| or
 // |-commandDispatchUsingKeyModifiers:| actions and a target of FirstResponder
 // in IB. If it's not one of those, let it continue up the responder chain to be
@@ skipping 300 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