Add Cross Process Guests feature switch to about:flags.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index e876e6247f92020e966908542c7c5696eae3fb1a..c9153420e56541cd86213d61eb49d5d3392dcb8a 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -13795,6 +13795,16 @@ Please check your email at <ph name="ACCOUNT_EMAIL">$2<ex>jane.doe@gmail.com</ex
         Highly experimental performance mode where cross-site iframes are kept in a separate process from the top document. In this mode, iframes from different third-party sites will be allowed to share a process.
       </message>
 
+      <!-- Cross process guest frames isolation mode -->
+      <message name="IDS_FLAGS_CROSS_PROCESS_GUEST_VIEW_ISOLATION_NAME"
+               desc="Name of about:flag option to turn on experimental guests using out-of-process iframes">
+        Cross process frames for guests
+      </message>
+      <message name="IDS_FLAGS_CROSS_PROCESS_GUEST_VIEW_ISOLATION_DESCRIPTION"
+               desc="Description of about:flag option to turn on experimental guests using out-of-process iframes">
+               Highly experimental where guests such as &lt;webview> are implemented on the out-of-process iframe infrastructure.
+      </message>
+
       <!-- Browser Task Scheduler -->
       <message name="IDS_FLAGS_BROWSER_TASK_SCHEDULER_NAME"
                desc="Name of about:flag option to control the availability of the browser task scheduler."