sync: preliminary support for deferred SyncBackendHost initialization

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 14799f4117082b029d65369dbc9fabdf8cc975ae..86d97347a811c22cbedc5b8b0a1c514d66360bca 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1297,6 +1297,10 @@ const char kSyncThrowUnrecoverableError[]   = "sync-throw-unrecoverable-error";
 // Tries to connect to XMPP using SSLTCP first (for testing).
 const char kSyncTrySsltcpFirstForXmpp[]     = "sync-try-ssltcp-first-for-xmpp";
 
+// Enables deferring sync backend initialization until user initiated changes
+// occur.
+const char kSyncEnableDeferredStartup[] = "sync-enable-deferred-startup";
+
 // Enables tab dragging to create a real browser.
 const char kTabBrowserDragging[]            = "enable-tab-browser-dragging";