Add support for virtual displays

ui/display/util/display_util.h

 // Copyright 2014 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_DISPLAY_UTIL_DISPLAY_UTIL_H_
 #define UI_DISPLAY_UTIL_DISPLAY_UTIL_H_
 
 #include "ui/display/util/display_util_export.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace ui {
 
 // Returns true if a given size is in the list of bogus sizes in mm that should
 // be ignored.
 DISPLAY_UTIL_EXPORT bool IsDisplaySizeBlackListed(
     const gfx::Size& physical_size);
 
 // Returns the desired device scale factor for the display with the given
 // physical_size and resoultion.
 DISPLAY_UTIL_EXPORT float GetScaleFactor(
     const gfx::Size& physical_size_in_mm,
     const gfx::Size& screen_size_in_pixels);
 
+// Returns 64-bit persistent ID for the specified manufacturer's ID and
+// product_code_hash, and the index of the output it is connected to.
+// |output_index| is used to distinguish the displays of the same type. For
+// example, swapping two identical display between two outputs will not be
+// treated as swap. The 'serial number' field in EDID isn't used here because
+// it is not guaranteed to have unique number and it may have the same fixed
+// value (like 0).
+DISPLAY_UTIL_EXPORT int64_t GenerateDisplayID(uint16_t manufacturer_id,
+                                              uint32_t product_code_hash,
+                                              uint8_t output_index);
+
 }  // namespace ui
 
 #endif  // UI_DISPLAY_UTIL_DISPLAY_UTIL_H_