[FedCM] Ship iframe support

This CL moves the FedCM iframe support bit to its own flag and enables
it by default.

Intent to Ship:
https://groups.google.com/a/chromium.org/g/blink-dev/c/IGvFrHYMH7A

Bug: 1322320
Change-Id: I8f45069a3d9ea220711de3d2243bb34af597ae69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4098644
Reviewed-by: Yi Gu <[email protected]>
Reviewed-by: Rick Byers <[email protected]>
Reviewed-by: Avi Drissman <[email protected]>
Commit-Queue: Nicolás Peña <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1083869}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index be438e6..002982c 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -1424,6 +1424,11 @@
 const char kFedCmDescription[] =
     "Enables JavaScript API to intermediate federated identity requests.";
 
+const char kFedCmIframeSupportName[] = "FedCM with iframe support";
+const char kFedCmIframeSupportDescription[] =
+    "Enables the 'identity-credentials-get' Permissions-Policy for the FedCM "
+    "API.";
+
 const char kFedCmWithoutThirdPartyCookiesName[] =
     "FedCmWithoutThirdPartyCookies";
 const char kFedCmWithoutThirdPartyCookiesDescription[] =