Call RemoveObserver in AndroidSigninManager

BUG=334424

Review URL: https://codereview.chromium.org/138673005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245367 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/android/signin/signin_manager_android.cc

@@ -210,6 +210,7 @@ void SigninManagerAndroid::OnBrowsingDataRemoverDone() {
 void SigninManagerAndroid::MergeSessionCompleted(
     const std::string& account_id,
     const GoogleServiceAuthError& error) {
+  merge_session_helper_->RemoveObserver(this);
   merge_session_helper_.reset();
 }