Add Cross Process Guests feature switch to about:flags.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 86d89ae2dd81bc8390d59a45650c70c3f6bc0acd..23e6c1582aecb03e315f2eaf6df79cb90075c602 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2119,6 +2119,9 @@ const FeatureEntry kFeatureEntries[] = {
     // NOTE: Adding new command-line switches requires adding corresponding
     // entries to enum "LoginCustomFlags" in histograms.xml. See note in
     // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.
+    {"cross-process-guests", IDS_FLAGS_CROSS_PROCESS_GUEST_VIEW_ISOLATION_NAME,
+     IDS_FLAGS_CROSS_PROCESS_GUEST_VIEW_ISOLATION_DESCRIPTION, kOsDesktop,
+     FEATURE_VALUE_TYPE(features::kGuestViewCrossProcessFrames)},
 };
 
 class FlagsStateSingleton {