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..718f922127538465eb33521d6d0a5bf3d5e91037 100644
--- a/components/autofill/core/common/autofill_util.cc
+++ b/components/autofill/core/common/autofill_util.cc
@@ -115,6 +115,12 @@ bool FieldIsSuggestionSubstringStartingOnTokenBoundary(
              base::string16::npos;
 }
 
+bool IsPrefixOfEmailEndingWithAtSign(const base::string16& full_string,
+                                     const base::string16& prefix) {
+  return base::StartsWith(full_string, prefix + base::UTF8ToUTF16("@"),
+                          base::CompareCase::SENSITIVE);
+}
+
 size_t GetTextSelectionStart(const base::string16& suggestion,
                              const base::string16& field_contents,
                              bool case_sensitive) {