Adds UKM for autofill attributes in form_structure.

components/autofill/core/browser/autofill_metrics.h

Index: components/autofill/core/browser/autofill_metrics.h
diff --git a/components/autofill/core/browser/autofill_metrics.h b/components/autofill/core/browser/autofill_metrics.h
index d0aba8221f6a042da66e97546fa6324a761df639..2c89a8667196151ace81d49cb2287d04de320f3c 100644
--- a/components/autofill/core/browser/autofill_metrics.h
+++ b/components/autofill/core/browser/autofill_metrics.h
@@ -27,6 +27,8 @@ namespace internal {
 // Name constants are exposed here so they can be referenced from tests.
 extern const char kUKMCardUploadDecisionEntryName[];
 extern const char kUKMCardUploadDecisionMetricName[];
+extern const char kUKMDeveloperEngagementEntryName[];
+extern const char kUKMDeveloperEngagementMetricName[];
 }  // namespace internal
 
 namespace autofill {
@@ -697,6 +699,13 @@ class AutofillMetrics {
       const GURL& url,
       AutofillMetrics::CardUploadDecisionMetric upload_decision);
 
+  // Logs the developer engagement ukm for the specified |url| and autofill
+  // fields in the form structure.
+  static void LogDeveloperEngagementUkm(
+      ukm::UkmService* ukm_service,
+      const GURL& url,
+      AutofillMetrics::DeveloperEngagementMetric form_structure_metric);
+
   // Logs the the |ukm_entry_name| with the specified |url| and the specified
   // |metrics|. Returns whether the ukm was sucessfully logged.
   static bool LogUkm(ukm::UkmService* ukm_service,