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..4bf719627d06feeab1ede28ec4aca59fef0fac53 100644
--- a/components/autofill/core/common/autofill_util.h
+++ b/components/autofill/core/common/autofill_util.h
@@ -51,10 +51,15 @@ 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,

[vabr (Chromium), 2017/06/12 18:56:58]

nit: I'm not sure what is the advantage of dropping "Field" from the name of
this function. It generates unnecessary churn in the code and confuses per-line
history with unrelated changes. Also the "field" from the name is reflected in
the "field" part of |field_contents|, with the latter making less sense now.

[melandory, 2017/06/19 10:53:48]

I brought old name back

+                                        const base::string16& field_contents,
+                                        bool case_sensitive);
+
+// Currently, a token for the purposes of this method is defined as {'@'}.

[vabr (Chromium), 2017/06/12 18:56:59]

nit: Redefining "token" for this method and keeping the old definition for the
methods above and below is confusing. Also, it is unlikely that more token
separators will be added for this function. I propose replacing "TokenBoundary"
with "AtSign".

[melandory, 2017/06/19 10:53:48]

Done.

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