Use ASCII case conversion in PasswordCredential.

It's what's expected per spec, and it's more efficient.

Bug: 627682
Change-Id: I5462a9c34cf9a1b6f2825e9e0c58e3c64b8c1698
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575034Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652477}

third_party/blink/renderer/modules/credentialmanager/password_credential.cc

@@ -61,7 +61,7 @@ PasswordCredential* PasswordCredential::Create(
     ToHTMLElement(submittable_element)
         ->FastGetAttribute(html_names::kAutocompleteAttr)
         .GetString()
-        .DeprecatedLower()
+        .LowerASCII()
         .Split(' ', autofill_tokens);
     for (const auto& token : autofill_tokens) {
       if (token == "current-password" || token == "new-password") {