Access SigninErrorProvider through ChromeBrowserProvider.

ios/public/provider/chrome/browser/chrome_browser_provider.h

Index: ios/public/provider/chrome/browser/chrome_browser_provider.h
diff --git a/ios/public/provider/chrome/browser/chrome_browser_provider.h b/ios/public/provider/chrome/browser/chrome_browser_provider.h
index ef57773fa2eed8a436a170b88f71268ca7d84566..b2610b35ff83da0b6157242896cca058292d9730 100644
--- a/ios/public/provider/chrome/browser/chrome_browser_provider.h
+++ b/ios/public/provider/chrome/browser/chrome_browser_provider.h
@@ -58,6 +58,7 @@ class ChromeBrowserProvider;
 class ChromeBrowserState;
 class ChromeIdentityService;
 class GeolocationUpdaterProvider;
+class SigninErrorProvider;
 class SigninResourcesProvider;
 class LiveTabContextProvider;
 class UpdatableResourceProvider;
@@ -86,6 +87,8 @@ class ChromeBrowserProvider {
   virtual InfoBarViewPlaceholder CreateInfoBarView(
       CGRect frame,
       InfoBarViewDelegate* delegate) NS_RETURNS_RETAINED;
+  // Returns an instance of a signing error provider.
+  virtual SigninErrorProvider* GetSigninErrorProvider();
   // Returns an instance of a signin resources provider.
   virtual SigninResourcesProvider* GetSigninResourcesProvider();
   // Sets the current instance of Chrome identity service. Used for testing.