Teach the GCM Driver how to decrypt incoming messages.

components/gcm_driver/crypto/gcm_message_cryptographer.cc

Index: components/gcm_driver/crypto/gcm_message_cryptographer.cc
diff --git a/components/gcm_driver/crypto/gcm_message_cryptographer.cc b/components/gcm_driver/crypto/gcm_message_cryptographer.cc
index 62b7247d41da5cffd26aa270cfa61a8bd9d0511c..a3bcfad1b7005b680786dac3dcb12567e3df5e05 100644
--- a/components/gcm_driver/crypto/gcm_message_cryptographer.cc
+++ b/components/gcm_driver/crypto/gcm_message_cryptographer.cc
@@ -23,13 +23,10 @@ const size_t kDefaultRecordSize = 4096;
 // Key size, in bytes, of a valid AEAD_AES_128_GCM key.
 const size_t kContentEncryptionKeySize = 16;
 
-// Salt size, in bytes, that will be used together with the key to create a
-// unique content encryption key for a given message.
-const size_t kSaltSize = 16;
-
 }  // namespace
 
 const size_t GCMMessageCryptographer::kAuthenticationTagBytes = 16;
+const size_t GCMMessageCryptographer::kSaltSize = 16;
 
 GCMMessageCryptographer::GCMMessageCryptographer() {}