Fixed PasswordIssuesMediatorTest.TestPasswordDeletion test

Test was flaky because objects in the test scope weren't deallocated
properly. Changing to BlockCleanupTest is fixing it.

Bug: 1126660
Change-Id: If301a7c27a6170b2a12831ea06c78e7f1e204a74
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2414230
Commit-Queue: Viktor Semeniuk <vsemeniuk@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808357}

ios/chrome/browser/ui/settings/password/password_issues_mediator_unittest.mm

@@ -85,10 +85,10 @@ CompromisedCredentials MakeCompromised(base::StringPiece signon_realm,
 @end
 
 // Tests for Password Issues mediator.
-class PasswordIssuesMediatorTest : public PlatformTest {
+class PasswordIssuesMediatorTest : public BlockCleanupTest {
  protected:
-  PasswordIssuesMediatorTest()
-      : task_environment_(base::test::TaskEnvironment::MainThreadType::UI) {
+  void SetUp() override {
+    BlockCleanupTest::SetUp();
     // Create BrowserState.
     TestChromeBrowserState::Builder test_cbs_builder;
     chrome_browser_state_ = test_cbs_builder.Build();