[autofill] Use StrongAlias's operator->() in LanguageCode

This change removes the member functions `empty()` and `length()` from
autofill::LanguageCode and migrates callers to use operator->() instead.

Bug: 1142413
Change-Id: Ie19e8b22d1e2c5a91599cfa488874ff75cf4bc19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2556520Reviewed-by: Christoph Schwering <schwering@google.com>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#831031}

components/autofill/core/browser/form_structure.cc

@@ -711,7 +711,7 @@ bool FormStructure::EncodeUploadRequest(
   upload->set_data_present(EncodeFieldTypes(available_field_types));
   upload->set_passwords_revealed(passwords_were_revealed_);
   upload->set_has_form_tag(is_form_tag_);
-  if (!page_language_.empty() && randomized_encoder_ != nullptr) {
+  if (!page_language_->empty() && randomized_encoder_ != nullptr) {
     upload->set_language(page_language_.value());
   }
 

components/autofill/core/common/language_code.h

@@ -29,12 +29,9 @@ class LanguageCode
   explicit LanguageCode(std::string&& s) : BaseClass(std::move(s)) { Check(); }
   explicit LanguageCode(const std::string& s) : BaseClass(s) { Check(); }
 
-  size_t length() const { return value().length(); }
-  bool empty() const { return value().empty(); }
-
  private:
   void Check() {
-    DCHECK((length() <= 3 && base::ranges::all_of(value(), &islower)) ||
+    DCHECK(((*this)->size() <= 3 && base::ranges::all_of(value(), &islower)) ||
            value() == "zh-CN" || value() == "zh-TW")
         << "Unexpected language code '" << value() << "'";
   }