Add mirrored screen option.
 This option flips scree image horizontally.

BUG=431731
[email protected]

Review URL: https://codereview.chromium.org/715543004

Cr-Commit-Position: refs/heads/master@{#304160}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 2200e28..9ba3b249 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1053,6 +1053,12 @@
     kOsCrOS,
     SINGLE_VALUE_TYPE(ash::switches::kAshDisableTextFilteringInOverviewMode),
   },
+  { "ash-enable-mirrored-screen",
+    IDS_FLAGS_ASH_ENABLE_MIRRORED_SCREEN_NAME,
+    IDS_FLAGS_ASH_ENABLE_MIRRORED_SCREEN_DESCRIPTION,
+    kOsCrOS,
+    SINGLE_VALUE_TYPE(ash::switches::kAshEnableMirroredScreen),
+  },
 #endif  // defined(USE_ASH)
 #if defined(OS_CHROMEOS)
   {