Don't add an aura tooltip to bubble close buttons on Windows.

ui/views/bubble/bubble_frame_view.cc

 // 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 "ui/views/bubble/bubble_frame_view.h"
 
 #include <algorithm>
 
 #include "ui/base/hit_test.h"
 #include "ui/base/l10n/l10n_util.h"
@@ skipping 87 matching lines @@
   ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
   LabelButton* close = new LabelButton(listener, base::string16());
   close->SetImage(CustomButton::STATE_NORMAL,
                   *rb.GetImageNamed(IDR_CLOSE_DIALOG).ToImageSkia());
   close->SetImage(CustomButton::STATE_HOVERED,
                   *rb.GetImageNamed(IDR_CLOSE_DIALOG_H).ToImageSkia());
   close->SetImage(CustomButton::STATE_PRESSED,
                   *rb.GetImageNamed(IDR_CLOSE_DIALOG_P).ToImageSkia());
   close->SetBorder(nullptr);
   close->SetSize(close->GetPreferredSize());
+#if !defined(OS_WIN)
+  // Windows will automatically create a tooltip for the close button based on
+  // the HTCLOSE result from NonClientHitTest().
   close->SetTooltipText(l10n_util::GetStringUTF16(IDS_APP_CLOSE));
+#endif
   return close;
 }
 
 gfx::Rect BubbleFrameView::GetBoundsForClientView() const {
   gfx::Rect client_bounds = GetLocalBounds();
   client_bounds.Inset(GetInsets());
   client_bounds.Inset(bubble_border_->GetInsets());
   return client_bounds;
 }
 
@@ skipping 305 matching lines @@
   if (titlebar_extra_view_ != NULL)
     title_bar_width += titlebar_extra_view_->GetPreferredSize().width();
   gfx::Size size(client_size);
   size.SetToMax(gfx::Size(title_bar_width, 0));
   const gfx::Insets insets(GetInsets());
   size.Enlarge(insets.width(), insets.height());
   return size;
 }
 
 }  // namespace views