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..c0d1064edb4765be235ca71b143ec126710052b0 100644
--- a/components/autofill/core/common/autofill_util.cc
+++ b/components/autofill/core/common/autofill_util.cc
@@ -34,6 +34,8 @@ namespace {
 
 const char kSplitCharacters[] = " .,-_@";
 
+const char kPrefixMatchTockens[] = "@";
+
 template <typename Char>
 struct Compare : base::CaseInsensitiveCompareASCII<Char> {
   explicit Compare(bool case_sensitive) : case_sensitive_(case_sensitive) {}
@@ -99,10 +101,9 @@ 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 +116,22 @@ bool FieldIsSuggestionSubstringStartingOnTokenBoundary(
              base::string16::npos;
 }
 
+bool IsPrefixStartingOnTokenBoundary(const base::string16& full_string,
+                                     const base::string16& prefix,
+                                     bool case_sensitive) {
+  if (base::StartsWith(full_string, prefix,
+                       case_sensitive ? base::CompareCase::SENSITIVE
+                                      : base::CompareCase::INSENSITIVE_ASCII)) {
+    if (full_string.size() > prefix.size()) {
+      char token = full_string[prefix.size()];
+
+      const std::string tokens(kPrefixMatchTockens);

[dvadym, 2017/06/01 12:15:56]

Since kPrefixMatchTockens is array only with 1 element, my feeling that it's
better to keep things simple and just make const char not const char[], that
would allow avoid creating a string here. Or you can even avoid creating a
constant by directly checking full_string[prefix.size()] == '@'.

If we ever decide to expand on another tokens, const array could be easily
added.

+      return tokens.find(token) != std::string::npos;
+    }
+  }
+  return false;
+}
+
 size_t GetTextSelectionStart(const base::string16& suggestion,
                              const base::string16& field_contents,
                              bool case_sensitive) {