[webcrypto] Reject AES-GCM tag lengths other than 32, 64, 96, 104, 112, 120, 128.

content/renderer/webcrypto/platform_crypto_nss.cc

 // Copyright 2014 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.
 
 #include "content/renderer/webcrypto/platform_crypto.h"
 
 #include <cryptohi.h>
 #include <pk11pub.h>
 #include <sechash.h>
 
@@ skipping 275 matching lines @@
 Status AesGcmEncryptDecrypt(EncryptOrDecrypt mode,
                             SymKey* key,
                             const CryptoData& data,
                             const CryptoData& iv,
                             const CryptoData& additional_data,
                             unsigned int tag_length_bits,
                             blink::WebArrayBuffer* buffer) {
   if (!g_aes_gcm_support.Get().IsSupported())
     return Status::ErrorUnsupported();
 
-  // TODO(eroman): Is this necessary?
-  if ((tag_length_bits % 8) != 0)
-    return Status::ErrorInvalidAesGcmTagLength();
   unsigned int tag_length_bytes = tag_length_bits / 8;
 
   CK_GCM_PARAMS gcm_params = {0};
   gcm_params.pIv = const_cast<unsigned char*>(iv.bytes());
   gcm_params.ulIvLen = iv.byte_length();
 
   gcm_params.pAAD = const_cast<unsigned char*>(additional_data.bytes());
   gcm_params.ulAADLen = additional_data.byte_length();
 
   gcm_params.ulTagBits = tag_length_bits;
@@ skipping 729 matching lines @@
                                      algorithm,
                                      usage_mask);
   return Status::Success();
 }
 
 }  // namespace platform
 
 }  // namespace webcrypto
 
 }  // namespace content