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.cc b/chrome/browser/flag_descriptions.cc
index a0cab2e0..bf0422e 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2810,6 +2810,12 @@
     "When enabled, Autofill suggestions' labels are displayed using a "
     "mobile-friendly format.";
 
+const char kAppMenuMobileSiteOptionName[] =
+    "Show Mobile Site option in app menu";
+const char kAppMenuMobileSiteOptionDescription[] =
+    "When enabled, app menu should show 'Mobile site' when showing desktop "
+    "site, instead of showing 'Desktop Site' with checkbox";
+
 const char kBackgroundTaskComponentUpdateName[] =
     "Background Task Component Updates";
 const char kBackgroundTaskComponentUpdateDescription[] =