Revert "[iOS] Disable signed-in account view controller"

This reverts commit 71e64b81.

Reason for revert: This CL is only needed to be tested on canary and then merged to M77. CL https://chromium-review.googlesource.com/c/chromium/src/+/1819247 is the fix intended for M78+.

Original change's description:
> [iOS] Disable signed-in account view controller
> 
> Disable the signed-in account view controller dialog.
> This patch is to disable it for M-77 and M-78. The right fix will
> come later with crbug.com/1006717
> 
> Bug: 1006744
> Change-Id: I537969bb221e165a7a0ca66d4324f8d87580916b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1819304
> Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
> Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#698946}

TBR=msarda@chromium.org,justincohen@chromium.org,jlebel@chromium.org

Change-Id: Ie6e9b97321b54d00b8ef3c2e600934e365fd9dc4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1006744
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1818528Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699237}

ios/chrome/browser/ui/authentication/signed_in_accounts_view_controller.mm

@@ -202,14 +202,10 @@ BOOL gSignedInAccountsViewControllerIsShown = NO;
   if (!browserState || browserState->IsOffTheRecord()) {
     return NO;
   }
-  // Temporary fix for regression for http://crbug.com/1006744: Disable showing
-  // the signed-in account modal dialog.
-  //
-  // AuthenticationService* authService =
-  //    AuthenticationServiceFactory::GetForBrowserState(browserState);
-  // return !gSignedInAccountsViewControllerIsShown &&
-  //       authService->IsAuthenticated() && authService->HaveAccountsChanged();
-  return NO;
+  AuthenticationService* authService =
+      AuthenticationServiceFactory::GetForBrowserState(browserState);
+  return !gSignedInAccountsViewControllerIsShown &&
+         authService->IsAuthenticated() && authService->HaveAccountsChanged();
 }
 
 #pragma mark Initialization

ios/chrome/browser/ui/authentication/signed_in_accounts_view_controller_unittest.mm

@@ -59,10 +59,8 @@ TEST_F(SignedInAccountsViewControllerTest,
 
 // Tests that the signed in accounts view should be presented when the accounts
 // have changed.
-// Temporary disabled for regression for http://crbug.com/1006744: Disable
-// showing the signed-in account modal dialog.
 TEST_F(SignedInAccountsViewControllerTest,
-       DISABLED_ShouldBePresentedForBrowserStateNecessary) {
+       ShouldBePresentedForBrowserStateNecessary) {
   auth_service_->SetHaveAccountsChanged(true);
   EXPECT_TRUE([SignedInAccountsViewController
       shouldBePresentedForBrowserState:browser_state_.get()]);