Cache a screen compatible DC to avoid re-creating it excessively.

ui/gfx/screen_compatible_dc_win.h

Index: ui/gfx/screen_compatible_dc_win.h
===================================================================
--- ui/gfx/screen_compatible_dc_win.h	(revision 0)
+++ ui/gfx/screen_compatible_dc_win.h	(revision 0)
@@ -0,0 +1,32 @@
+// 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_SCREEN_COMPATIBLE_DC_WIN_H_
+#define UI_GFX_SCREEN_COMPATIBLE_DC_WIN_H_
+#pragma once
+
+#include <windows.h>
+
+#include "base/basictypes.h"
+
+namespace gfx {
+
+// Temporary device context that is compatible with the screen. Can be used for
+// short-lived operations on the UI threads.
+class ScopedTemporaryScreenCompatibleDC {
+ public:
+  ScopedTemporaryScreenCompatibleDC();
+  ~ScopedTemporaryScreenCompatibleDC();
+
+  operator HDC() { return hdc_; }

[sky, 2012/02/03 23:14:42]

Is there a reason you like this better than a static getter?
We generally avoid operators like this.

[Alexei Svitkine (slow), 2012/02/06 14:37:38]

I based this off of base::win::ScopedCreateDC, which also has the HDC operator.
Let me know if you prefer me to change this to a HDC get() method instead.

I decided to make it a scoper because it will make it easy to add debugging code
to check for overlapping uses if we ever suspect someone is using this outside
the UI thread or in an overlapping fashion...

[sky, 2012/02/06 16:43:08]

The style guide recommends against it, so I say go with get.

+
+ private:
+  HDC hdc_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedTemporaryScreenCompatibleDC);
+};
+
+}  // namespace gfx
+
+#endif  // UI_GFX_SCREEN_COMPATIBLE_DC_WIN_H_