Added UMA statistics for change passwords in the Password Manager

components/password_manager/core/browser/password_manager_client.h

Index: components/password_manager/core/browser/password_manager_client.h
diff --git a/components/password_manager/core/browser/password_manager_client.h b/components/password_manager/core/browser/password_manager_client.h
index 00ebc140297d666e858c26f216572f82820361e1..84623ff2fe8b6aa57ffc971f9040b855e3e789cf 100644
--- a/components/password_manager/core/browser/password_manager_client.h
+++ b/components/password_manager/core/browser/password_manager_client.h
@@ -73,6 +73,18 @@ class PasswordManagerClient {
   // password store if the user allows it. The embedder is not required to
   // prompt the user if it decides that this form doesn't need to be saved or
   // updated. Returns true if the prompt was indeed displayed.
+  // There are 3 different cases when |update_password| == true:
+  // 1.Change password form was submitted and the user has only one stored

[vasilii, 2015/08/21 14:59:22]

"A change password form" here and below.

[dvadym, 2015/08/21 15:31:13]

Done.

+  // credential. Then form_to_save.pending_credentials() should correspond to
+  // the unique element from |form_to_save.best_matches_|.
+  // 2.Change password form was submitted and the user has more than one stored
+  // credential. Then we shouldn't expact anything from

[vasilii, 2015/08/21 14:59:22]

expect

[dvadym, 2015/08/21 15:31:13]

Done.

+  // form_to_save.pending_credentials() except correct origin, since we don't
+  // know which credentials should be update.

[vasilii, 2015/08/21 14:59:22]

updated

[dvadym, 2015/08/21 15:31:13]

Done.

+  // 3.Sign-in password form was submitted with a password different from

[vasilii, 2015/08/21 14:59:22]

A sign-in

[dvadym, 2015/08/21 15:31:13]

Done.

+  // stored one. In this case form_to_save.password_overridden() == true and

[vasilii, 2015/08/21 14:59:22]

the stored one

[dvadym, 2015/08/21 15:31:13]

Done.

+  // form_to_save.pending_credentials() should correspond to the credential that
+  // was overidden.
   virtual bool PromptUserToSaveOrUpdatePassword(
       scoped_ptr<PasswordFormManager> form_to_save,
       CredentialSourceType type,