DialogDelegate: allow platforms to prevent Cancel being default

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 20 matching lines @@
 #endif
 
 }  // namespace
 
 #if !defined(OS_MACOSX)
 
 const int PlatformStyle::kComboboxNormalArrowPadding = 7;
 const int PlatformStyle::kMinLabelButtonWidth = 70;
 const int PlatformStyle::kMinLabelButtonHeight = 33;
 const bool PlatformStyle::kDefaultLabelButtonHasBoldFont = true;
+const bool PlatformStyle::kDialogDefaultButtonCanBeCancel = true;
 const bool PlatformStyle::kTextfieldDragVerticallyDragsToEnd = false;
 const CustomButton::NotifyAction PlatformStyle::kMenuNotifyActivationAction =
     CustomButton::NOTIFY_ON_RELEASE;
 
 // static
 gfx::ImageSkia PlatformStyle::CreateComboboxArrow(bool is_enabled,
                                                   Combobox::Style style) {
   ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
   return *rb.GetImageSkiaNamed(IDR_MENU_DROPARROW);
 }
@@ skipping 58 matching lines @@
 
 #if !defined(DESKTOP_LINUX)
 // static
 std::unique_ptr<Border> PlatformStyle::CreateThemedLabelButtonBorder(
     LabelButton* button) {
   return button->CreateDefaultBorder();
 }
 #endif
 
 }  // namespace views