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 721b34d0b3705d727cf11710ae03ea78edb6e472..fbe95ca98fb8a04d640d46375244941c26cdad8f 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1323,6 +1323,10 @@ 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";