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..a2026e4477599f99b5d9aa5dd88a88aa6f191862 100644
--- a/components/autofill/core/common/autofill_util.h
+++ b/components/autofill/core/common/autofill_util.h
@@ -51,10 +51,16 @@ bool IsHintEnabledInKeyboardAccessory();
 // Returns true if the |field_contents| is a substring of the |suggestion|
 // starting at token boundaries. |field_contents| can span multiple |suggestion|
 // tokens.
-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);
+
+// Currently, a token for the purposes of this method is defined as {'@'}.
+// Returns true if the |full_string| has a |prefix| as a prefix and the prefix
+// end on a token.

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

prefix end -> prefix ends

[melandory, 2017/06/12 14:56:12]

Done.

+bool IsPrefixStartingOnTokenBoundary(const base::string16& full_string,

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

As far as I understand |prefix| should end at Token, so probably name something
like IsPrefixEndingOnTokenBoundary is more correct.

[melandory, 2017/06/12 14:56:12]

Done.

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