Add ability to set resolution on external display

ash/display/display_util_x11.h

+// Copyright (c) 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.
+
+#ifndef ASH_DISPLAY_DISPLAY_UTIL_X11_H_
+#define ASH_DISPLAY_DISPLAY_UTIL_X11_H_
+
+#include <vector>
+
+#include "ash/ash_export.h"
+#include "ash/display/display_info.h"
+
+struct _XRRScreenResources;
+typedef _XRRScreenResources XRRScreenResources;
+struct _XRROutputInfo;
+typedef _XRROutputInfo XRROutputInfo;
+
+namespace ash {
+namespace internal {
+struct Resolution;
+
+// Returns true if the size info in the output_info isn't valid
+// and should be ignored. This is exposed for testing.
+// |mm_width| and |mm_height| are given in millimeters.
+ASH_EXPORT bool ShouldIgnoreSize(unsigned long mm_width,
+                                 unsigned long mm_height);
+
+// Returns the resolution list.
+ASH_EXPORT std::vector<Resolution> GetResolutionList(
+    XRRScreenResources* screen_resources,
+    XRROutputInfo* output_info);
+
+}  // namespace internal
+}  // namespace ash
+
+#endif  // ASH_DISPLAY_DISPLAY_UTIL_X11_H_