[Android][Test] Simplify identity manager test with AccountManagerTestRule

This CL simplifies identity manager tests' setup with
AccountManagerTestRule.

Bug: 1120301
Change-Id: I9ee0af5a144b582739a87b53dd8f8cd73c6eed44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2369093Reviewed-by: Tanmoy Mollik <triploblastic@chromium.org>
Commit-Queue: Alice Wang <aliceywang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801787}

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

@@ -16,8 +16,6 @@ import org.junit.runner.RunWith;
 import org.chromium.base.test.BaseJUnit4ClassRunner;
 import org.chromium.chrome.browser.profiles.Profile;
 import org.chromium.chrome.test.util.browser.signin.AccountManagerTestRule;
-import org.chromium.components.signin.AccountManagerFacadeProvider;
-import org.chromium.components.signin.base.CoreAccountId;
 import org.chromium.components.signin.base.CoreAccountInfo;
 import org.chromium.components.signin.identitymanager.IdentityManager;
 import org.chromium.components.signin.identitymanager.IdentityMutator;
@@ -48,8 +46,8 @@ public class IdentityManagerIntegrationTest {
 
     @Before
     public void setUp() {
-        mTestAccount1 = createCoreAccountInfoFromEmail(TEST_ACCOUNT1);
-        mTestAccount2 = createCoreAccountInfoFromEmail(TEST_ACCOUNT2);
+        mTestAccount1 = mAccountManagerTestRule.toCoreAccountInfo(TEST_ACCOUNT1);
+        mTestAccount2 = mAccountManagerTestRule.toCoreAccountInfo(TEST_ACCOUNT2);
 
         NativeLibraryTestUtils.loadNativeLibraryAndInitBrowserProcess();
 
@@ -62,12 +60,6 @@ public class IdentityManagerIntegrationTest {
         });
     }
 
-    private static CoreAccountInfo createCoreAccountInfoFromEmail(String accountEmail) {
-        String accountGaiaId =
-                AccountManagerFacadeProvider.getInstance().getAccountGaiaId(accountEmail);
-        return new CoreAccountInfo(new CoreAccountId(accountGaiaId), accountEmail, accountGaiaId);
-    }
-
     @After
     public void tearDown() {
         TestThreadUtils.runOnUiThreadBlocking(