Autofill: Set requirements for number of recognized fields in an autofillable form

components/autofill/core/browser/form_field.cc

Index: components/autofill/core/browser/form_field.cc
diff --git a/components/autofill/core/browser/form_field.cc b/components/autofill/core/browser/form_field.cc
index 191be8d62f4d80459c572f0179a930c0afde2e18..b5229d1665b645be481868fa55cb1e56171ce5c6 100644
--- a/components/autofill/core/browser/form_field.cc
+++ b/components/autofill/core/browser/form_field.cc
@@ -40,6 +40,7 @@ bool ShouldBeIgnored(const AutofillField* field) {
 
 // static
 void FormField::ParseFormFields(const std::vector<AutofillField*>& fields,
+                                bool is_in_form_tag,
                                 ServerFieldTypeMap* map) {
   // Set up a working copy of the fields to be processed.
   std::vector<AutofillField*> remaining_fields(fields.size());
@@ -50,8 +51,11 @@ void FormField::ParseFormFields(const std::vector<AutofillField*>& fields,
                      ShouldBeIgnored),
       remaining_fields.end());
 
+  ServerFieldTypeMap saved_map = *map;
+
   // Email pass.
   ParseFormFieldsPass(EmailField::Parse, &remaining_fields, map);
+  size_t email_count = map->size();
 
   // Phone pass.
   ParseFormFieldsPass(PhoneField::Parse, &remaining_fields, map);
@@ -64,6 +68,17 @@ void FormField::ParseFormFields(const std::vector<AutofillField*>& fields,
 
   // Name pass.
   ParseFormFieldsPass(NameField::Parse, &remaining_fields, map);
+
+  // Do not autofill a form if there are less than 3 recognized fields.
+  // Otherwise it is very easy to have false positives. http://crbug.com/447332
+  // For <form> tags, make an exception for email fields, which are commonly the
+  // only recognized field on account registration sites.
+  size_t count = map->size();
+  size_t kThreshold = 3;
+  bool accept_parsing = (count >= kThreshold ||
+                         (is_in_form_tag && email_count > 0));
+  if (!accept_parsing)
+    *map = saved_map;
 }
 
 // static
@@ -130,17 +145,17 @@ bool FormField::Match(const AutofillField* field,
                       const base::string16& pattern,
                       int match_type) {
   if ((match_type & FormField::MATCH_LABEL) &&
-      autofill::MatchesPattern(field->label, pattern)) {
+      MatchesPattern(field->label, pattern)) {
     return true;
   }
 
   if ((match_type & FormField::MATCH_NAME) &&
-      autofill::MatchesPattern(field->name, pattern)) {
+      MatchesPattern(field->name, pattern)) {
     return true;
   }
 
   if ((match_type & FormField::MATCH_VALUE) &&
-      autofill::MatchesPattern(field->value, pattern)) {
+      MatchesPattern(field->value, pattern)) {
     return true;
   }