Put Sync Encryption UI behind command line switch.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 14765b84630ee50bebacfaff57794489371cb659..13f7b3fb7fea8620992ced4592d469baa387e56d 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -504,6 +504,9 @@ const char kEnableSync[]                    = "enable-sync";
 // Enable syncing browser autofill.
 const char kEnableSyncAutofill[]            = "enable-sync-autofill";
 
+// Enable sync encryption options.
+const char kEnableSyncEncryption[]          = "enable-sync-encryption";
+
 // Enable syncing browser sessions.
 const char kEnableSyncSessions[]            = "enable-sync-sessions";