Use std::unique_ptr to pass around WebCryptoDigestor.

components/webcrypto/webcrypto_impl.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 "components/webcrypto/webcrypto_impl.h"
 
 #include <limits.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 745 matching lines @@
     blink::WebCryptoResult result) {
   std::unique_ptr<DeriveKeyState> state(
       new DeriveKeyState(algorithm, base_key, import_algorithm,
                          key_length_algorithm, extractable, usages, result));
   if (!CryptoThreadPool::PostTask(
           FROM_HERE, base::Bind(DoDeriveKey, base::Passed(&state)))) {
     CompleteWithThreadPoolError(&result);
   }
 }
 
-blink::WebCryptoDigestor* WebCryptoImpl::createDigestor(
+std::unique_ptr<blink::WebCryptoDigestor> WebCryptoImpl::createDigestor(
     blink::WebCryptoAlgorithmId algorithm_id) {
-  return webcrypto::CreateDigestor(algorithm_id).release();
+  return webcrypto::CreateDigestor(algorithm_id);
 }
 
 bool WebCryptoImpl::deserializeKeyForClone(
     const blink::WebCryptoKeyAlgorithm& algorithm,
     blink::WebCryptoKeyType type,
     bool extractable,
     blink::WebCryptoKeyUsageMask usages,
     const unsigned char* key_data,
     unsigned key_data_size,
     blink::WebCryptoKey& key) {
   return webcrypto::DeserializeKeyForClone(
       algorithm, type, extractable, usages,
       webcrypto::CryptoData(key_data, key_data_size), &key);
 }
 
 bool WebCryptoImpl::serializeKeyForClone(
     const blink::WebCryptoKey& key,
     blink::WebVector<unsigned char>& key_data) {
   return webcrypto::SerializeKeyForClone(key, &key_data);
 }
 
 }  // namespace webcrypto