Improve computing autcomplete attributes in utils.

Autocomplete attributes are string properties of DOM elements. For
parsing password forms, a few special values are important.

This CL adds a few functions to password_form_conversion_utils to
compute an enum representation of the autocomplete attributes, and a
simple cache to keep those computed values to minimize string
comparisons.

Bug: 833838
Change-Id: I6c386895be9af54ae1e31c715795a26b29eb0e5c
Reviewed-on: https://chromium-review.googlesource.com/1027881Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Commit-Queue: Vaclav Brozek <vabr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561441}

components/autofill/content/renderer/password_autofill_agent.cc

@@ -167,10 +167,12 @@ bool HasPasswordWithAutocompleteAttribute(
 
     const blink::WebInputElement input_element =
         control_element.ToConst<blink::WebInputElement>();
+    const AutocompleteFlag flag = AutocompleteFlagForElement(input_element);
     if (input_element.IsPasswordFieldForAutofill() &&
-        (HasAutocompleteAttributeValue(input_element, "current-password") ||
-         HasAutocompleteAttributeValue(input_element, "new-password")))
+        (flag == AutocompleteFlag::CURRENT_PASSWORD ||
+         flag == AutocompleteFlag::NEW_PASSWORD)) {
       return true;
+    }
   }
 
   return false;
@@ -232,7 +234,8 @@ bool FindFormInputElement(
     // set. Also make sure we avoid keeping password fields having
     // |autocomplete='new-password'| attribute set.
     if (ambiguous_and_multiple_password_fields_with_autocomplete &&
-        !HasAutocompleteAttributeValue(input_element, "current-password")) {
+        AutocompleteFlagForElement(input_element) !=
+            AutocompleteFlag::CURRENT_PASSWORD) {
       continue;
     }
 
@@ -591,7 +594,7 @@ bool ShouldShowStandaloneManuallFallback(const blink::WebInputElement& element,
   return (
       element.IsPasswordFieldForAutofill() &&
       !IsCreditCardVerificationPasswordField(element) &&
-      !HasCreditCardAutocompleteAttributes(element) &&
+      AutocompleteFlagForElement(element) != AutocompleteFlag::CREDIT_CARD &&
       !base::StartsWith(url.scheme(), "chrome", base::CompareCase::SENSITIVE) &&
       !url.SchemeIs(url::kAboutScheme) &&
       base::FeatureList::IsEnabled(
@@ -922,7 +925,7 @@ bool PasswordAutofillAgent::IsUsernameOrPasswordField(
     return true;
 
   // If a field declares itself a username input, show the warning.
-  if (HasAutocompleteAttributeValue(element, "username"))
+  if (AutocompleteFlagForElement(element) == AutocompleteFlag::USERNAME)
     return true;
 
   // Otherwise, analyze the form and return true if this input element seems

components/autofill/content/renderer/password_form_conversion_utils.h

@@ -42,6 +42,20 @@ enum UsernameDetectionMethod {
   USERNAME_DETECTION_METHOD_COUNT
 };
 
+// The susbset of autocomplete flags related to passwords.
+enum class AutocompleteFlag {
+  NONE,
+  USERNAME,
+  CURRENT_PASSWORD,
+  NEW_PASSWORD,
+  // Represents the whole family of cc-* flags.
+  CREDIT_CARD
+};
+
+// Returns the AutocompleteFlag derived from |element|'s autocomplete attribute.
+AutocompleteFlag AutocompleteFlagForElement(
+    const blink::WebInputElement& element);
+
 // The caller of this function is responsible for deleting the returned object.
 re2::RE2* CreateMatcher(void* instance, const char* pattern);
 
@@ -81,15 +95,6 @@ std::unique_ptr<PasswordForm> CreatePasswordFormFromUnownedInputElements(
     const FormsPredictionsMap* form_predictions,
     UsernameDetectorCache* username_detector_cache);
 
-// Checks in a case-insensitive way if the autocomplete attribute for the given
-// |element| is present and has the specified |value_in_lowercase|.
-bool HasAutocompleteAttributeValue(const blink::WebInputElement& element,
-                                   base::StringPiece value_in_lowercase);
-
-// Checks in a case-insensitive way if credit card autocomplete attributes for
-// the given |element| are present.
-bool HasCreditCardAutocompleteAttributes(const blink::WebInputElement& element);
-
 // Returns whether the form |field| has a "password" type, but looks like a
 // credit card verification field.
 bool IsCreditCardVerificationPasswordField(const blink::WebInputElement& field);

components/autofill/content/renderer/password_generation_agent.cc

@@ -99,7 +99,8 @@ std::vector<blink::WebInputElement> FindNewPasswordElementsMarkedBySite(
   std::vector<blink::WebInputElement> passwords;
 
   auto is_new_password_field = [](const blink::WebInputElement& element) {
-    return HasAutocompleteAttributeValue(element, "new-password");
+    return AutocompleteFlagForElement(element) ==
+           AutocompleteFlag::NEW_PASSWORD;
   };
 
   auto field_iter =