Add the Sign-At-Most-Once restriction the enterprise.platformKeys API.

chrome/browser/chromeos/platform_keys/platform_keys.h

Index: chrome/browser/chromeos/platform_keys/platform_keys.h
diff --git a/chrome/browser/chromeos/platform_keys/platform_keys.h b/chrome/browser/chromeos/platform_keys/platform_keys.h
index de27fb4610741ef88fdc5b0aee3f65b01ce584a9..a2b0ad631c22a1791f1c2b42068318c648be5f0e 100644
--- a/chrome/browser/chromeos/platform_keys/platform_keys.h
+++ b/chrome/browser/chromeos/platform_keys/platform_keys.h
@@ -24,10 +24,11 @@ namespace chromeos {
 
 namespace platform_keys {
 
-// If the generation was successful, |public_key_spki_der| will contain the DER
-// encoding of the SubjectPublicKeyInfo of the generated key and |error_message|
-// will be empty. If it failed, |public_key_spki_der| will be empty and
-// |error_message| contain an error message.
+namespace subtle {

[pneubeck (no reviews), 2014/06/10 17:50:11]

I could move these functions to another file.
But to simplify the review, I put them into a namespace at first.

+// Functions of this namespace shouldn't be called directly from the context of
+// an extension. Instead use PlatfromKeysService which enforces restrictions

[eroman, 2014/06/12 05:50:45]

typeo Platfrom -> Platform

[pneubeck (no reviews), 2014/06/12 09:21:36]

Done.

+// upon extensions.
+
 typedef base::Callback<void(const std::string& public_key_spki_der,
                             const std::string& error_message)>
     GenerateKeyCallback;
@@ -40,9 +41,6 @@ void GenerateRSAKey(const std::string& token_id,
                     const GenerateKeyCallback& callback,
                     Profile* profile);
 
-// If signing was successful, |signature| will be contain the signature and
-// |error_message| will be empty. If it failed, |signature| will be empty and
-// |error_message| contain an error message.
 typedef base::Callback<void(const std::string& signature,
                             const std::string& error_message)> SignCallback;
 
@@ -58,6 +56,8 @@ void Sign(const std::string& token_id,
           const SignCallback& callback,
           Profile* profile);
 
+}  // namespace subtle
+
 // If the list of certificates could be successfully retrieved, |certs| will
 // contain the list of available certificates (maybe empty) and |error_message|
 // will be empty. If an error occurred, |certs| will be empty and