Add new flag for consistent identity.

components/signin/core/common/signin_switches.cc

Index: components/signin/core/common/signin_switches.cc
diff --git a/components/signin/core/common/signin_switches.cc b/components/signin/core/common/signin_switches.cc
index 892de989d57c9353996866ef82f346fb35e68f72..4216d5cb875f794972b1df8606a87583e08fcd38 100644
--- a/components/signin/core/common/signin_switches.cc
+++ b/components/signin/core/common/signin_switches.cc
@@ -10,6 +10,9 @@ namespace switches {
 // expiration of credentials during testing.
 const char kClearTokenService[] = "clear-token-service";
 
+// Enables consistent identity features.
+const char kEnableAccountConsistency[] = "enable-account-consistency";
+
 // Enables the pure web-based flow for sign in on first run/NTP/wrench menu/
 // settings page.
 const char kEnableWebBasedSignin[] = "enable-web-based-signin";