[Autofill] Use field signatures as a fallback to retrieve cached fields.

The usage of Java script in forms can result in unstable renderer ids
and therefore cache misses. This is mitigated by using unique-only field
signatures as a fallback.

Change-Id: Icae0f719c8ad1ea4de9dd9ab142b0d6aa746b2ab
Bug: 1087386, 1091401
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2396141Reviewed-by: Christoph Schwering <schwering@google.com>
Commit-Queue: Matthias Körber <koerber@google.com>
Cr-Commit-Position: refs/heads/master@{#805806}

components/autofill/core/browser/form_structure.cc

@@ -1115,6 +1115,30 @@ void FormStructure::RetrieveFromCache(
         cached_field = it->second;
     }
 
+    // If the unique renderer id (or the name) is not stable due to some Java
+    // Script magic in the website, use the field signature as a fallback
+    // solution to find the field in the cached form.
+    // TODO(crbug.com/1125624): Remove feature check once trial ended.
+    if (!cached_field &&
+        base::FeatureList::IsEnabled(
+            features::kAutofillRetrieveFromCacheWithFieldSignatureAsFallback)) {
+      // Iterates over the fields to find the field with the same form
+      // signature.
+      for (size_t i = 0; i < cached_form.field_count(); ++i) {
+        auto* const cfield = cached_form.field(i);
+        if (field->GetFieldSignature() == cfield->GetFieldSignature()) {
+          // If there are multiple matches, do not retrieve the field and stop
+          // the process.
+          if (cached_field) {
+            cached_field = nullptr;
+            break;
+          } else {
+            cached_field = cfield;
+          }
+        }
+      }
+    }
+
     if (cached_field) {
       if (!only_server_and_autofill_state) {
         // Transfer attributes of the cached AutofillField to the newly created

components/autofill/core/common/autofill_features.cc

@@ -159,6 +159,13 @@ const base::Feature kAutofillRetrieveFromCacheWithRendererIds{
     "AutofillRetrieveFromCacheWithRendererIds",
     base::FEATURE_DISABLED_BY_DEFAULT};
 
+// When enabled, Autofill will try to retrieve cached fields by signatures as a
+// fallback that is useful if unique renderer ids are unstable.
+// TODO(crbug.com/1125624): Remove experiment once trial ended.
+const base::Feature kAutofillRetrieveFromCacheWithFieldSignatureAsFallback{
+    "AutofillRetrieveFromCacheWithFieldSignatureAsFallback",
+    base::FEATURE_DISABLED_BY_DEFAULT};
+
 // When enabled, autofill suggestions are displayed in the keyboard accessory
 // instead of the regular popup.
 const base::Feature kAutofillKeyboardAccessory{

components/autofill/core/common/autofill_features.h

@@ -45,6 +45,8 @@ extern const base::Feature kAutofillFixFillableFieldTypes;
 extern const base::Feature kAutofillImportPrefilledCountryAndStateValues;
 extern const base::Feature kAutofillKeepInitialFormValuesInCache;
 extern const base::Feature kAutofillRetrieveFromCacheWithRendererIds;
+extern const base::Feature
+    kAutofillRetrieveFromCacheWithFieldSignatureAsFallback;
 extern const base::Feature kAutofillKeyboardAccessory;
 extern const base::Feature kAutofillLabelAffixRemoval;
 extern const base::Feature kAutofillPruneSuggestions;