Use std::unique_ptr to pass around WebCryptoDigestor.

third_party/WebKit/Source/platform/Crypto.h

 // 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.
 
 // TODO(jww) The original Blink-style header guard for this file conflicts with
 // the header guard in Source/modules/crypto/Crypto.h, so this is a
 // Chromium-style header guard instead. There is now a bug
 // (https://crbug.com/360121) to track a proposal to change all header guards
 // to a similar style. Thus, whenever that is resolved, this header guard
 // should be changed to whatever style is agreed upon.
@@ skipping 15 matching lines @@
 
 const size_t sha1HashSize = 20;
 enum HashAlgorithm {
     HashAlgorithmSha1,
     HashAlgorithmSha256,
     HashAlgorithmSha384,
     HashAlgorithmSha512
 };
 
 PLATFORM_EXPORT bool computeDigest(HashAlgorithm, const char* digestable, size_t length, DigestValue& digestResult);
+// Note: this will never return null.
 PLATFORM_EXPORT std::unique_ptr<WebCryptoDigestor> createDigestor(HashAlgorithm);
 PLATFORM_EXPORT void finishDigestor(WebCryptoDigestor*, DigestValue& digestResult);
 
 } // namespace blink
 
 namespace WTF {
 
 struct DigestValueHash {
     STATIC_ONLY(DigestValueHash);
     static unsigned hash(const blink::DigestValue& v)
@@ skipping 17 matching lines @@
     STATIC_ONLY(DefaultHash);
     typedef IntHash<blink::HashAlgorithm> Hash;
 };
 template <>
 struct HashTraits<blink::HashAlgorithm> : UnsignedWithZeroKeyHashTraits<blink::HashAlgorithm> {
     STATIC_ONLY(HashTraits);
 };
 
 } // namespace WTF
 #endif // SOURCE_PLATFORM_CRYPTO_H_