Teach PasswordAutofillAgent sometimes match prefixes of usernames

components/autofill/core/common/autofill_util.cc

Index: components/autofill/core/common/autofill_util.cc
diff --git a/components/autofill/core/common/autofill_util.cc b/components/autofill/core/common/autofill_util.cc
index 50e50176d8c336e700bef8af1c7e6bfd865250fd..b1c86d36203a6ac4dab6ab4a646a7dec92c66f54 100644
--- a/components/autofill/core/common/autofill_util.cc
+++ b/components/autofill/core/common/autofill_util.cc
@@ -99,10 +99,9 @@ bool IsHintEnabledInKeyboardAccessory() {
 #endif
 }
 
-bool FieldIsSuggestionSubstringStartingOnTokenBoundary(
-    const base::string16& suggestion,
-    const base::string16& field_contents,
-    bool case_sensitive) {
+bool IsSubstringStartingOnTokenBoundary(const base::string16& suggestion,
+                                        const base::string16& field_contents,
+                                        bool case_sensitive) {
   if (!IsFeatureSubstringMatchEnabled()) {
     return base::StartsWith(suggestion, field_contents,
                             case_sensitive
@@ -115,6 +114,15 @@ bool FieldIsSuggestionSubstringStartingOnTokenBoundary(
              base::string16::npos;
 }
 
+bool IsPrefixEndingOnTokenBoundary(const base::string16& full_string,
+                                   const base::string16& prefix) {
+  if (base::StartsWith(full_string, prefix, base::CompareCase::SENSITIVE)) {
+    return (full_string.size() > prefix.size() &&
+            full_string[prefix.size()] == '@');
+  }
+  return false;
+}
+
 size_t GetTextSelectionStart(const base::string16& suggestion,
                              const base::string16& field_contents,
                              bool case_sensitive) {