[Signin][Android] Forbid signin when Primary Account is set

This adds a failing assert when SigninManager.Signin is triggered while
the primary account is already set in IdentityManager.

Bug: 995201
Change-Id: Ib404f930694ea82aada3bac5a144dac096fa1541
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1824267Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Pâris Meuleman <pmeuleman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707298}

chrome/android/java/src/org/chromium/chrome/browser/signin/SigninManager.java

@@ -459,6 +459,9 @@ public class SigninManager
         // This method should be called at most once per sign-in flow.
         assert mSignInState != null && mSignInState.mCoreAccountInfo != null;
 
+        // The user should not be already signed in
+        assert !mIdentityManager.hasPrimaryAccount();
+
         if (!mIdentityMutator.setPrimaryAccount(mSignInState.mCoreAccountInfo.getId())) {
             Log.w(TAG, "Failed to set the PrimaryAccount in IdentityManager, aborting signin");
             abortSignIn();

chrome/android/junit/src/org/chromium/chrome/browser/signin/SigninManagerTest.java

@@ -222,6 +222,7 @@ public class SigninManagerTest {
         doReturn(account)
                 .when(mIdentityManager)
                 .findExtendedAccountInfoForAccountWithRefreshTokenByEmailAddress(any());
+        doReturn(false).when(mIdentityManager).hasPrimaryAccount();
         doReturn(true).when(mIdentityMutator).setPrimaryAccount(any());
         doNothing().when(mIdentityMutator).reloadAllAccountsFromSystemWithPrimaryAccount(any());
 
@@ -237,4 +238,30 @@ public class SigninManagerTest {
         assertFalse(mSigninManager.isOperationInProgress());
         assertEquals(1, callCount.get());
     }
+
+    @Test(expected = AssertionError.class)
+    public void failIfAlreadySignedin() {
+        CoreAccountInfo account = new CoreAccountInfo(new CoreAccountId("test_at_gmail.com"),
+                new Account("test@gmail.com", AccountManagerFacade.GOOGLE_ACCOUNT_TYPE),
+                "test_at_gmail.com");
+
+        // No need to seed accounts to the native code.
+        doReturn(true).when(mAccountTrackerService).checkAndSeedSystemAccounts();
+        // Request that policy is loaded. It will pause sign-in until onPolicyCheckedBeforeSignIn is
+        // invoked.
+        doNothing().when(mNativeMock).fetchAndApplyCloudPolicy(anyLong(), any(), any());
+
+        doReturn(account)
+                .when(mIdentityManager)
+                .findExtendedAccountInfoForAccountWithRefreshTokenByEmailAddress(any());
+        doReturn(true).when(mIdentityManager).hasPrimaryAccount();
+
+        mSigninManager.onFirstRunCheckDone(); // Allow sign-in.
+
+        mSigninManager.signIn(account.getAccount(), null);
+        assertTrue(mSigninManager.isOperationInProgress());
+
+        // The following should throw an assertion error
+        mSigninManager.finishSignInAfterPolicyEnforced();
+    }
 }