Reland of Reimplement AccountManagerHelper singleton instance creation

chrome/android/javatests/src/org/chromium/chrome/browser/signin/OAuth2TokenServiceTest.java

 // 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.
 
 package org.chromium.chrome.browser.signin;
 
 import android.accounts.Account;
 import android.support.test.InstrumentationRegistry;
 import android.support.test.filters.SmallTest;
 
+import org.junit.After;
 import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
 import org.chromium.base.test.util.AdvancedMockContext;
 import org.chromium.base.test.util.DisabledTest;
 import org.chromium.base.test.util.Feature;
 import org.chromium.chrome.test.ChromeJUnit4ClassRunner;
 import org.chromium.components.signin.AccountManagerHelper;
@@ skipping 12 matching lines @@
     @Before
     public void setUp() throws Exception {
         // Mock out the account manager on the device.
         mContext = new AdvancedMockContext(
                 InstrumentationRegistry.getInstrumentation().getTargetContext());
         mAccountManager = new MockAccountManager(
                 mContext, InstrumentationRegistry.getInstrumentation().getContext());
         AccountManagerHelper.overrideAccountManagerHelperForTests(mContext, mAccountManager);
     }
 
+    @After
+    public void tearDown() {
+        AccountManagerHelper.resetAccountManagerHelperForTests();
+    }
+
     /*
      *  @SmallTest
      *  @Feature({"Sync"})
      */
     @Test
     @DisabledTest(message = "crbug.com/533417")
     public void testGetAccountsNoAccountsRegistered() {
         String[] accounts = OAuth2TokenService.getAccounts();
         Assert.assertEquals("There should be no accounts registered", 0, accounts.length);
     }
@@ skipping 68 matching lines @@
                                               .hasBeenAccepted(oauth2Scope, true)
                                               .authToken(oauth2Scope, expectedToken)
                                               .build();
         mAccountManager.addAccountHolderExplicitly(accountHolder);
 
         String accessToken = OAuth2TokenService.getOAuth2AccessTokenWithTimeout(
                 mContext, account, scope, 5, TimeUnit.SECONDS);
         Assert.assertEquals(expectedToken, accessToken);
     }
 }