[Android] Replace a synchronous callsite of GetAccounts()

chrome/browser/android/signin/account_tracker_service_android.h

 // Copyright 2015 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 CHROME_BROWSER_ANDROID_SIGNIN_ACCOUNT_TRACKER_SERVICE_ANDROID_H_
 #define CHROME_BROWSER_ANDROID_SIGNIN_ACCOUNT_TRACKER_SERVICE_ANDROID_H_
 
 #include <jni.h>
 
-#include "base/android/scoped_java_ref.h"
-#include "chrome/browser/profiles/profile.h"
-#include "components/signin/core/browser/account_tracker_service.h"
+namespace signin {
+namespace android {
+// A bridge between the Java and C++ AccountTrackerService.
+bool RegisterAccountTrackerService(JNIEnv* env);
 
-// Android wrapper of the AccountTrackerService which provides access from Java
-// layer. Note that on Android, there's only a single profile, and therefore a
-// single instance of this wrapper. The same name of the Java class is
-// AccountTrackerService.
-class AccountTrackerServiceAndroid {
- public:
-  AccountTrackerServiceAndroid(JNIEnv* env, jobject obj);
-
-  // Registers the AccountTrackerServiceAndroid's native methods through JNI.
-  static bool Register(JNIEnv* env);
-
-  void SeedAccountsInfo(JNIEnv* env,
-                        jobject obj,
-                        jobjectArray gaiaIds,
-                        jobjectArray accountNames);
-
- private:
-  ~AccountTrackerServiceAndroid();
-
-  base::android::ScopedJavaGlobalRef<jobject> java_account_tracker_service_;
-};
+}  // namespace android
+}  // namespace signin
 
 #endif  // CHROME_BROWSER_ANDROID_SIGNIN_ACCOUNT_TRACKER_SERVICE_ANDROID_H_