Add ui::GrabDesktopSnapshot for Windows.

ui/snapshot/test/snapshot_desktop_win.cc

+// Copyright 2013 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/snapshot/test/snapshot_desktop.h"
+
+#include "ui/snapshot/snapshot_win.h"
+
+namespace ui {
+
+bool GrabDesktopSnapshot(const gfx::Rect& snapshot_bounds,
+                         std::vector<unsigned char>* png_representation) {
+  return internal::GrabHwndSnapshot(NULL, snapshot_bounds, png_representation);
+}
+
+}  // namespace ui