Force Account Consistency off for Logout call on iOS.

ios/chrome/browser/signin/gaia_auth_fetcher_ios.mm

Index: ios/chrome/browser/signin/gaia_auth_fetcher_ios.mm
diff --git a/ios/chrome/browser/signin/gaia_auth_fetcher_ios.mm b/ios/chrome/browser/signin/gaia_auth_fetcher_ios.mm
index 7722186e6d942a48f5b3b7fec535e2a9630500e4..ce8d7343bf633fed028477c43d172dcde43b3558 100644
--- a/ios/chrome/browser/signin/gaia_auth_fetcher_ios.mm
+++ b/ios/chrome/browser/signin/gaia_auth_fetcher_ios.mm
@@ -320,7 +320,12 @@ GaiaAuthFetcherIOS::GaiaAuthFetcherIOS(GaiaAuthConsumer* consumer,
                                        web::BrowserState* browser_state)
     : GaiaAuthFetcher(consumer, source, getter),
       bridge_(new GaiaAuthFetcherIOSBridge(this, browser_state)),
-      browser_state_(browser_state) {}
+      browser_state_(browser_state) {
+  // Account Consistency needs to be disabled for the Logout call. There is a
+  // race with the cookie clearing request (handled by
+  // AccountConsistencyService), so we invalidate the cookie for the call.
+  SetLogoutHeaders("Cookie: X-CHROME-CONNECTED=EXPIRED;");
+}
 
 GaiaAuthFetcherIOS::~GaiaAuthFetcherIOS() {
 }