[Passwords] Reject Empty Usernames for Leak Detection

This change implements logic rejecting forms with empty usernames for
the leak detection feature. Also it adds a DCHECK that the password is
non-empty.

Bug: 986298
Change-Id: I178da166e0f7c0f9baa17ad6ed1452446c2e998e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1763692Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689024}

components/password_manager/core/browser/leak_detection_delegate.cc

@@ -30,9 +30,14 @@ void LeakDetectionDelegate::StartLeakCheck(const autofill::PasswordForm& form) {
     return;
 
   if (!client_->GetPrefs()->GetBoolean(
-          password_manager::prefs::kPasswordLeakDetectionEnabled))
+          password_manager::prefs::kPasswordLeakDetectionEnabled)) {
+    return;
+  }
+
+  if (form.username_value.empty())
     return;
 
+  DCHECK(!form.password_value.empty());
   leak_check_ = leak_factory_->TryCreateLeakCheck(
       this, client_->GetIdentityManager(), client_->GetURLLoaderFactory());
   if (leak_check_) {

components/password_manager/core/browser/leak_detection_delegate_unittest.cc

@@ -110,6 +110,16 @@ TEST_F(LeakDetectionDelegateTest, PrefIsFalse) {
   EXPECT_FALSE(delegate().leak_check());
 }
 
+TEST_F(LeakDetectionDelegateTest, UsernameIsEmpty) {
+  autofill::PasswordForm form = CreateTestForm();
+  form.username_value.clear();
+
+  EXPECT_CALL(factory(), TryCreateLeakCheck).Times(0);
+  delegate().StartLeakCheck(form);
+
+  EXPECT_FALSE(delegate().leak_check());
+}
+
 TEST_F(LeakDetectionDelegateTest, StartCheck) {
   const autofill::PasswordForm form = CreateTestForm();
   EXPECT_CALL(client(), IsIncognito).WillOnce(Return(false));

components/password_manager/core/browser/password_manager.cc

@@ -1186,7 +1186,7 @@ void PasswordManager::OnLoginSuccessful() {
 
   client_->GetStoreResultFilter()->ReportFormLoginSuccess(*submitted_manager);
 #if !defined(OS_IOS)
-  leak_delegate_.StartLeakCheck(*submitted_manager->GetSubmittedForm());
+  leak_delegate_.StartLeakCheck(submitted_manager->GetPendingCredentials());
 #endif
 
   auto submission_event =