Mac: Fix Sierra solid color layer color-mismatch

ui/gfx/native_widget_types.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 UI_GFX_NATIVE_WIDGET_TYPES_H_
 #define UI_GFX_NATIVE_WIDGET_TYPES_H_
 
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 177 matching lines @@
 // Note: for test_shell we're packing a pointer into the NativeViewId. So, if
 // you make it a type which is smaller than a pointer, you have to fix
 // test_shell.
 //
 // See comment at the top of the file for usage.
 typedef intptr_t NativeViewId;
 
 // AcceleratedWidget provides a surface to compositors to paint pixels.
 #if defined(OS_WIN)
 typedef HWND AcceleratedWidget;
-const AcceleratedWidget kNullAcceleratedWidget = NULL;
+constexpr AcceleratedWidget kNullAcceleratedWidget = NULL;
 #elif defined(USE_X11)
 typedef unsigned long AcceleratedWidget;
-const AcceleratedWidget kNullAcceleratedWidget = 0;
+constexpr AcceleratedWidget kNullAcceleratedWidget = 0;
 #elif defined(OS_IOS)
 typedef UIView* AcceleratedWidget;
-const AcceleratedWidget kNullAcceleratedWidget = 0;
+constexpr AcceleratedWidget kNullAcceleratedWidget = 0;
 #elif defined(OS_MACOSX)
 typedef NSView* AcceleratedWidget;
-const AcceleratedWidget kNullAcceleratedWidget = 0;
+constexpr AcceleratedWidget kNullAcceleratedWidget = 0;
 #elif defined(OS_ANDROID)
 typedef ANativeWindow* AcceleratedWidget;
-const AcceleratedWidget kNullAcceleratedWidget = 0;
+constexpr AcceleratedWidget kNullAcceleratedWidget = 0;
 #elif defined(USE_OZONE)
 typedef int32_t AcceleratedWidget;
-const AcceleratedWidget kNullAcceleratedWidget = 0;
+constexpr AcceleratedWidget kNullAcceleratedWidget = 0;
 #else
 #error unknown platform
 #endif
 
 }  // namespace gfx
 
 #endif  // UI_GFX_NATIVE_WIDGET_TYPES_H_