Add a flag for the password manager force-saving experiment.

There is no functionality behind this flag yet.

I kept the name "force-saving", since this name of the feature is quite established now, although I wonder whether saying "manually save" wouldn't be more understandable in the description.

BUG=484891

Review URL: https://codereview.chromium.org/1140043003

Cr-Commit-Position: refs/heads/master@{#330438}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9d576acc..19c8ac7 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1153,6 +1153,14 @@
     SINGLE_VALUE_TYPE(switches::kDisablePasswordManagerReauthentication)
   },
   {
+    "enable-password-force-saving",
+    IDS_FLAGS_ENABLE_PASSWORD_FORCE_SAVING_NAME,
+    IDS_FLAGS_ENABLE_PASSWORD_FORCE_SAVING_DESCRIPTION,
+    kOsAll,
+    SINGLE_VALUE_TYPE(
+        password_manager::switches::kEnablePasswordForceSaving)
+  },
+  {
     "enable-password-link",
     IDS_FLAGS_PASSWORD_MANAGER_LINK_NAME,
     IDS_FLAGS_PASSWORD_MANAGER_LINK_DESCRIPTION,