[Autofill/Autocomplete Feature] Substring matching instead of prefix matching.

components/password_manager/core/browser/password_autofill_manager.h

Index: components/password_manager/core/browser/password_autofill_manager.h
diff --git a/components/password_manager/core/browser/password_autofill_manager.h b/components/password_manager/core/browser/password_autofill_manager.h
index 89bfd2debbe0c6c7f9bd397d182c2a0500407a15..c2a1543c06e9f3b48da9e02a9820ab76f1911e4f 100644
--- a/components/password_manager/core/browser/password_autofill_manager.h
+++ b/components/password_manager/core/browser/password_autofill_manager.h
@@ -32,7 +32,8 @@ class PasswordAutofillManager : public autofill::AutofillPopupDelegate {
   void OnPopupShown() override;
   void OnPopupHidden() override;
   void DidSelectSuggestion(const base::string16& value,
-                           int identifier) override;
+                           int identifier,
+                           size_t match_start) override;
   void DidAcceptSuggestion(const base::string16& value,
                            int identifier,
                            int position) override;
@@ -64,7 +65,9 @@ class PasswordAutofillManager : public autofill::AutofillPopupDelegate {
   bool FillSuggestionForTest(int key, const base::string16& username);
 
   // A public version of PreviewSuggestion(), only for use in tests.
-  bool PreviewSuggestionForTest(int key, const base::string16& username);
+  bool PreviewSuggestionForTest(int key,
+                                const base::string16& username,
+                                size_t match_start);
 
  private:
   typedef std::map<int, autofill::PasswordFormFillData> LoginToPasswordInfoMap;
@@ -75,7 +78,9 @@ class PasswordAutofillManager : public autofill::AutofillPopupDelegate {
 
   // Attempts to preview the password associated with user name |username|, and
   // returns true if it was successful.
-  bool PreviewSuggestion(int key, const base::string16& username);
+  bool PreviewSuggestion(int key,
+                         const base::string16& username,
+                         size_t match_start);
 
   // If |current_username| matches a username for one of the login mappings in
   // |fill_data|, returns true and assigns the password and the original signon