Teach PasswordAutofillAgent sometimes match prefixes of usernames

components/autofill/core/common/autofill_util.h

Index: components/autofill/core/common/autofill_util.h
diff --git a/components/autofill/core/common/autofill_util.h b/components/autofill/core/common/autofill_util.h
index 6a67f3ef8704ff75be3fe2617000abbd6e7cf3ef..f9f549c0a92abd1fa170db956d5eef2128201c4e 100644
--- a/components/autofill/core/common/autofill_util.h
+++ b/components/autofill/core/common/autofill_util.h
@@ -56,6 +56,12 @@ bool FieldIsSuggestionSubstringStartingOnTokenBoundary(
     const base::string16& field_contents,
     bool case_sensitive);
 
+// Currently, a token for the purposes of this method is defined as {'@'}.

[vabr (Chromium), 2017/06/19 12:54:15]

nit: Please update the comment not to mention any tokens, just inline '@'.

+// Returns true if the |full_string| has a |prefix| as a prefix and the prefix
+// ends on a token.
+bool IsPrefixOfEmailEndingAtSign(const base::string16& full_string,

[vabr (Chromium), 2017/06/19 12:54:15]

nit: EndingAtSign -> EndingWithAtSign

(The current name has an ambiguous use of "at", let's make clear "At" is meant
as the name of the sign.)

[melandory, 2017/06/21 12:00:42]

Done.

+                                 const base::string16& prefix);
+
 // Finds the first occurrence of a searched substring |field_contents| within
 // the string |suggestion| starting at token boundaries and returns the index to
 // the end of the located substring, or base::string16::npos if the substring is