Allow ChromeIdentityService in ChromeBrowserProvider to be overriden.

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 271cf814954b5b726f445f8648c350816ff65423..4b11a5502daf0fb008cbc7fdc041d0daa1b9a304 100644
--- a/ios/public/provider/chrome/browser/chrome_browser_provider.h
+++ b/ios/public/provider/chrome/browser/chrome_browser_provider.h
@@ -80,6 +80,9 @@ class ChromeBrowserProvider {
       InfoBarViewDelegate* delegate) NS_RETURNS_RETAINED;
   // Returns an instance of a signin resources provider.
   virtual SigninResourcesProvider* GetSigninResourcesProvider();
+  // Sets the current instance of Chrome identity service. Used for testing.
+  virtual void SetChromeIdentityServiceForTesting(
+      std::unique_ptr<ChromeIdentityService> service);
   // Returns an instance of a Chrome identity service.
   virtual ChromeIdentityService* GetChromeIdentityService();
   // Returns an instance of a LiveTabContextProvider.