[Autofill] Add Chrome flag that annotates web forms with form and field signatures

components/autofill/core/common/autofill_switches.cc

Index: components/autofill/core/common/autofill_switches.cc
diff --git a/components/autofill/core/common/autofill_switches.cc b/components/autofill/core/common/autofill_switches.cc
index 8aadec54c6211bd48e9461abfd15e4fd58050ead..217408a99d80ee84df1e96355a26a36a19fdb2a5 100644
--- a/components/autofill/core/common/autofill_switches.cc
+++ b/components/autofill/core/common/autofill_switches.cc
@@ -56,6 +56,9 @@ const char kLocalHeuristicsOnlyForPasswordGeneration[] =
 // Annotates forms with Autofill field type predictions.
 const char kShowAutofillTypePredictions[]   = "show-autofill-type-predictions";
 
+// Annotates forms and fields with Autofill signatures.
+const char kShowAutofillSignatures[] = "show-autofill-signatures";
+
 // Use the sandbox Online Wallet service URL (for developer testing).
 const char kWalletServiceUseSandbox[]       = "wallet-service-use-sandbox";