Eliminate CHECK from CryptohomeLibrary::LoadSystemSalt

chromeos/cryptohome/cryptohome_library.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROMEOS_CRYPTOHOME_CRYPTOHOME_LIBRARY_H_
 #define CHROMEOS_CRYPTOHOME_CRYPTOHOME_LIBRARY_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 41 matching lines @@
   virtual void TpmClearStoredPassword() = 0;
 
   virtual bool InstallAttributesGet(const std::string& name,
                                     std::string* value) = 0;
   virtual bool InstallAttributesSet(const std::string& name,
                                     const std::string& value) = 0;
   virtual bool InstallAttributesFinalize() = 0;
   virtual bool InstallAttributesIsInvalid() = 0;
   virtual bool InstallAttributesIsFirstInstall() = 0;
 
-  // Returns system hash in hex encoded ascii format.
+  // Returns system hash in hex encoded ascii format. Note: this may return
+  // an empty string (e.g. if cryptohome is not running). It is up to the
+  // calling function to try again after a delay if desired.
   virtual std::string GetSystemSalt() = 0;
 
   // Encrypts |token| with the system salt key (stable for the lifetime
   // of the device).  Useful to avoid storing plain text in place like
   // Local State.
   virtual std::string EncryptWithSystemSalt(const std::string& token) = 0;
 
   // Decrypts |token| with the system salt key (stable for the lifetime
   // of the device).
   virtual std::string DecryptWithSystemSalt(
       const std::string& encrypted_token_hex) = 0;
 
  protected:
   CryptohomeLibrary();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CryptohomeLibrary);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_CRYPTOHOME_CRYPTOHOME_LIBRARY_H_