Stupid....

chrome/browser/cocoa/download_shelf_controller.mm

 // Copyright (c) 2009 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.
 
 #import "download_shelf_controller.h"
 
 #include "app/l10n_util.h"
 #include "base/mac_util.h"
 #include "base/sys_string_conversions.h"
 #import "chrome/browser/cocoa/browser_window_controller.h"
@@ skipping 74 matching lines @@
 - (void)resizeDownloadShelf {
   NSRect barFrame = [[self view] frame];
   barFrame.origin.y = 0;
   barFrame.size.height = NSMinY([contentArea_ frame]);
   [[self view] setFrame:barFrame];
 }
 
 // Show or hide the bar based on the value of |enable|. Handles animating the
 // resize of the content view.
 - (void)showDownloadShelf:(BOOL)enable {
+  if ([self isVisible] == enable)
+    return;
+
   contentAreaHasOffset_ = enable;
   [[self view] setHidden:enable ? NO : YES];
   [self applyContentAreaOffset:enable];
 
   barIsVisible_ = enable;
 }
 
 // Apply a contents box offset to make (or remove) room for the
 // download shelf.  If apply==YES, always make room (the contentView_ is
 // "full size").  If apply==NO we are trying to undo an offset.  If no
@@ skipping 32 matching lines @@
 
 - (void)hide:(id)sender {
   [self showDownloadShelf:NO];
 }
 
 - (void)addDownloadItem:(NSView*)view {
   [[self view] addSubview:view];
 }
 
 @end