Update the "Desktop site" menu item

Instead of showing "Desktop site" with checkbox, we change it to show
"Request desktop site" and "Request mobile site".
Also update the user action related to the menu item. The user action is
already defined in actions.xml by IOS.

UX Mockups: go/clank-rds-ux

Bug: 1197164
Change-Id: Ic4ec4386d511edd308e1317d2ac51c7b78e94a49
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2813458
Commit-Queue: Gang Wu <[email protected]>
Reviewed-by: Theresa  <[email protected]>
Cr-Commit-Position: refs/heads/master@{#871058}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 2ac0ca4..c4efa5b6 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1633,6 +1633,9 @@
 extern const char kAutofillUseMobileLabelDisambiguationName[];
 extern const char kAutofillUseMobileLabelDisambiguationDescription[];
 
+extern const char kAppMenuMobileSiteOptionName[];
+extern const char kAppMenuMobileSiteOptionDescription[];
+
 extern const char kBackgroundTaskComponentUpdateName[];
 extern const char kBackgroundTaskComponentUpdateDescription[];