mac: Remove uses of a CoreGraphics private API that causes WindowServer crashes.

chrome/browser/ui/cocoa/constrained_window/constrained_window_custom_sheet.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_COCOA_CONSTRAINED_WINDOW_CONSTRAINED_WINDOW_CUSTOM_SHEET_H_
 #define CHROME_BROWSER_UI_COCOA_CONSTRAINED_WINDOW_CONSTRAINED_WINDOW_CUSTOM_SHEET_H_
 
 #import <Cocoa/Cocoa.h>
 
 #import "base/mac/scoped_nsobject.h"
 #import "chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet.h"
 
 // Represents a custom sheet. The sheet's window is shown without using the
 // system |beginSheet:...| API.
 @interface CustomConstrainedWindowSheet : NSObject<ConstrainedWindowSheet> {
  @protected
   base::scoped_nsobject<NSWindow> customWindow_;
+  BOOL useSimpleAnimations_;
 }
 
 - (id)initWithCustomWindow:(NSWindow*)customWindow;
 
+// Defaults to NO.
+// The standard animation uses private CGS APIs, which can crash the window
+// server. https://crbug.com/515627#c75
+- (void)setUseSimpleAnimations:(BOOL)simpleAnimations;
+
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_CONSTRAINED_WINDOW_CONSTRAINED_WINDOW_CUSTOM_SHEET_H_