Compute if sign out is allowed on every app startup.

The existing sign out pref is written just once, which makes sense for Android
EDU devices, but not for child accounts. These accounts may become
unsupervised, in which case they should be able to sign out.

Test: verified that the "Sign out of Chrome" button is hidden while an
existing consumer account is supervised, and enabled after the account chooses
to leave supervision. Didn't test on an Android EDU device yet.

Bug: 894618
Change-Id: I81e4f75857bf7f8346ef4a48caa3e32edae95848
Reviewed-on: https://chromium-review.googlesource.com/c/1306654Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Commit-Queue: P H <phongo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606059}

chrome/android/java/src/org/chromium/chrome/browser/firstrun/ForcedSigninProcessor.java

@@ -18,7 +18,6 @@ import org.chromium.chrome.browser.signin.SigninManager;
 import org.chromium.chrome.browser.util.FeatureUtilities;
 import org.chromium.components.signin.AccountManagerFacade;
 import org.chromium.components.signin.ChildAccountStatus;
-import org.chromium.components.signin.ChromeSigninController;
 
 import javax.annotation.Nullable;
 
@@ -48,17 +47,19 @@ public final class ForcedSigninProcessor {
      * changes with early exit if an account has already been signed in.
      */
     public static void start(final Context appContext, @Nullable final Runnable onComplete) {
-        if (ChromeSigninController.get().isSignedIn()) return;
         new AndroidEduAndChildAccountHelper() {
             @Override
             public void onParametersReady() {
                 boolean isAndroidEduDevice = isAndroidEduDevice();
                 boolean hasChildAccount = ChildAccountStatus.isChild(getChildAccountStatus());
-                // If neither a child account or and EDU device, we return.
-                if (!isAndroidEduDevice && !hasChildAccount) return;
                 // Child account and EDU device at the same time is not supported.
                 assert !(isAndroidEduDevice && hasChildAccount);
-                processForcedSignIn(appContext, onComplete);
+
+                boolean forceSignin = isAndroidEduDevice || hasChildAccount;
+                AccountManagementFragment.setSignOutAllowedPreferenceValue(!forceSignin);
+                if (forceSignin) {
+                    processForcedSignIn(appContext, onComplete);
+                }
             }
         }.start();
     }
@@ -86,8 +87,6 @@ public final class ForcedSigninProcessor {
                 signinManager.signIn(accounts[0], null, new SigninManager.SignInCallback() {
                     @Override
                     public void onSignInComplete() {
-                        // Since this is a forced signin, signout is not allowed.
-                        AccountManagementFragment.setSignOutAllowedPreferenceValue(false);
                         if (onComplete != null) {
                             onComplete.run();
                         }