Allow ChromeIdentityService in ChromeBrowserProvider to be overriden.

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

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IOS_PUBLIC_PROVIDER_CHROME_BROWSER_TEST_CHROME_BROWSER_PROVIDER_H_
 #define IOS_PUBLIC_PROVIDER_CHROME_BROWSER_TEST_CHROME_BROWSER_PROVIDER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 
 namespace ios {
 
 class TestUpdatableResourceProvider;
 
 class TestChromeBrowserProvider : public ChromeBrowserProvider {
  public:
   TestChromeBrowserProvider();
   ~TestChromeBrowserProvider() override;
 
   // Returns the current provider as a |TestChromeBrowserProvider|.
   static TestChromeBrowserProvider* GetTestProvider();
 
   // ChromeBrowserProvider:
+  void SetChromeIdentityServiceForTesting(
+      std::unique_ptr<ChromeIdentityService> service) override;
   ChromeIdentityService* GetChromeIdentityService() override;
   UpdatableResourceProvider* GetUpdatableResourceProvider() override;
 
  private:
   std::unique_ptr<ChromeIdentityService> chrome_identity_service_;
   std::unique_ptr<TestUpdatableResourceProvider>
       test_updatable_resource_provider_;
 
   DISALLOW_COPY_AND_ASSIGN(TestChromeBrowserProvider);
 };
 
 }  // namespace ios
 
 #endif  // IOS_PUBLIC_PROVIDER_CHROME_BROWSER_TEST_CHROME_BROWSER_PROVIDER_H_