[iOS] Saving empty username no longer crashed app

This change fixes the crash when username was changed to the empty one.

Bug: 1147046
Change-Id: I0c9e24bce474639499865c06f1d9007776bc5c6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2526323
Commit-Queue: Viktor Semeniuk <vsemeniuk@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825816}

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

@@ -38,7 +38,10 @@
       _website = base::SysUTF8ToNSString(nameWithLink.second.spec());
       _changePasswordURL = password_manager::CreateChangePasswordUrl(form.url);
     }
-    _username = base::SysUTF16ToNSString(form.username_value);
+
+    if (!form.blocked_by_user) {
+      _username = base::SysUTF16ToNSString(form.username_value);
+    }
 
     if (form.federation_origin.opaque()) {
       _password = base::SysUTF16ToNSString(form.password_value);

ios/chrome/browser/ui/settings/password/password_details/password_details_table_view_controller.mm

@@ -155,8 +155,8 @@ typedef NS_ENUM(NSInteger, ReauthenticationReason) {
   [model addItem:[self websiteItem]
       toSectionWithIdentifier:SectionIdentifierPassword];
 
-  // Blocked password forms don't have username value.
-  if ([self.password.username length]) {
+  // Blocked password forms have username equal to nil.
+  if (self.password.username != nil) {
     self.usernameTextItem = [self usernameItem];
     [model addItem:self.usernameTextItem
         toSectionWithIdentifier:SectionIdentifierPassword];

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

@@ -1482,6 +1482,21 @@ void CopyPasswordDetailWithID(int detail_id) {
   [[EarlGrey selectElementWithMatcher:PasswordDetailUsername()]
       assertWithMatcher:grey_textFieldValue(@"concrete username")];
 
+  // Empty username should work as well.
+  [[EarlGrey selectElementWithMatcher:PasswordDetailUsername()]
+      performAction:grey_replaceText(@"")];
+
+  [[EarlGrey selectElementWithMatcher:NavigationBarDoneButton()]
+      performAction:grey_tap()];
+
+  [[EarlGrey selectElementWithMatcher:EditConfirmationButton()]
+      performAction:grey_tap()];
+
+  [[EarlGrey selectElementWithMatcher:PasswordDetailUsername()]
+      assertWithMatcher:grey_textFieldValue(@"")];
+
+  TapEdit();
+
   [[EarlGrey selectElementWithMatcher:PasswordDetailUsername()]
       performAction:grey_replaceText(@"new username")];