Add support for virtual displays

ui/display/util/display_util.h

Index: ui/display/util/display_util.h
diff --git a/ui/display/util/display_util.h b/ui/display/util/display_util.h
index 012269d1038062fe189eb2e4416fe9c6930faff6..1eb4750c09e9735e0e368313154bff6e5009fa34 100644
--- a/ui/display/util/display_util.h
+++ b/ui/display/util/display_util.h
@@ -21,6 +21,17 @@ 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_