Add and use gfx::ScopedNSGraphicsContextState (ui/gfx/scoped_ns_graphics_context_state_mac.h).

ui/gfx/scoped_ns_graphics_context_save_gstate_mac.mm

+// Copyright (c) 2011 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/gfx/scoped_ns_graphics_context_save_gstate_mac.h"
+
+#include <AppKit/AppKit.h>
+
+namespace gfx {
+
+ScopedNSGraphicsContextSaveGState::ScopedNSGraphicsContextSaveGState(
+    NSGraphicsContext* context) : context_([context retain]) {
+  if (!context_)
+    context_.reset([[NSGraphicsContext currentContext] retain]);
+  [context_ saveGraphicsState];
+}
+
+ScopedNSGraphicsContextSaveGState::~ScopedNSGraphicsContextSaveGState() {
+  [context_ restoreGraphicsState];
+}
+
+}  // namespace gfx