views: don't use open-folder icons in TreeView on Mac

ui/views/style/platform_style.cc

 // Copyright 2015 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/style/platform_style.h"
 
 #include "base/memory/ptr_util.h"
 #include "build/build_config.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/base/resource/resource_bundle.h"
@@ skipping 31 matching lines @@
 const bool PlatformStyle::kDefaultLabelButtonHasBoldFont = true;
 const bool PlatformStyle::kDialogDefaultButtonCanBeCancel = true;
 const bool PlatformStyle::kSelectWordOnRightClick = false;
 const bool PlatformStyle::kSelectAllOnRightClickWhenUnfocused = false;
 const CustomButton::NotifyAction PlatformStyle::kMenuNotifyActivationAction =
     CustomButton::NOTIFY_ON_RELEASE;
 const CustomButton::KeyClickAction PlatformStyle::kKeyClickActionOnSpace =
     CustomButton::CLICK_ON_KEY_RELEASE;
 const bool PlatformStyle::kReturnClicksFocusedControl = true;
 const bool PlatformStyle::kTreeViewSelectionPaintsEntireRow = false;
+const bool PlatformStyle::kTreeViewUsesOpenIcon = true;
 const bool PlatformStyle::kUseRipples = true;
 const bool PlatformStyle::kMirrorBubbleArrowInRTLByDefault = true;
 
 // static
 gfx::ImageSkia PlatformStyle::CreateComboboxArrow(bool is_enabled,
                                                   Combobox::Style style) {
   ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
   return *rb.GetImageSkiaNamed(IDR_MENU_DROPARROW);
 }
 
@@ skipping 35 matching lines @@
 
 #if !defined(DESKTOP_LINUX)
 // static
 std::unique_ptr<Border> PlatformStyle::CreateThemedLabelButtonBorder(
     LabelButton* button) {
   return button->CreateDefaultBorder();
 }
 #endif
 
 }  // namespace views