[Android settings] Break the infinite re-spawning of reauth screen

This change adds a safeguard in PasswordReauthenticationFragment against
repeated showing of the screen lock.

If PasswordReauthenticationFragment gets killed during displaying the screen
lock, this CL ensures that it won't attempt to display it again on re-creation.

Bug: 791652
Change-Id: I7cc593906017bd059c6a4f3bd2b88d9b68488398
Reviewed-on: https://chromium-review.googlesource.com/806044
Commit-Queue: Vaclav Brozek <vabr@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522395}

chrome/android/java/src/org/chromium/chrome/browser/preferences/password/PasswordReauthenticationFragment.java

@@ -32,7 +32,8 @@ public class PasswordReauthenticationFragment extends Fragment {
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         mFragmentManager = getFragmentManager();
-        if (!sPreventLockDevice) {
+        boolean isFirstTime = savedInstanceState == null;
+        if (!sPreventLockDevice && isFirstTime) {
             lockDevice();
         }
     }