Implement hash function prioritization for SRI.

Source/core/frame/SubresourceIntegrity.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.
 
 #ifndef SubresourceIntegrity_h
 #define SubresourceIntegrity_h
 
 #include "core/CoreExport.h"
 #include "platform/Crypto.h"
 
@@ skipping 16 matching lines @@
     };
 
     static bool CheckSubresourceIntegrity(const Element&, const WTF::String& content, const KURL& resourceUrl, const Resource&);
 
 private:
     // FIXME: After the merge with the Chromium repo, this should be refactored
     // to use FRIEND_TEST in base/gtest_prod_util.h.
     friend class SubresourceIntegrityTest;
     friend class SubresourceIntegrityTest_Parsing_Test;
     friend class SubresourceIntegrityTest_ParseAlgorithm_Test;
+    friend class SubresourceIntegrityTest_Prioritization_Test;
 
     enum AlgorithmParseResult {
         AlgorithmValid,
         AlgorithmUnparsable,
         AlgorithmUnknown
     };
 
     struct IntegrityMetadata {
         WTF::String digest;
         HashAlgorithm algorithm;
     };
 
+    static HashAlgorithm getPrioritizedHashFunction(HashAlgorithm, HashAlgorithm);
     static AlgorithmParseResult parseAlgorithm(const UChar*& begin, const UChar* end, HashAlgorithm&);
     static bool parseDigest(const UChar*& begin, const UChar* end, String& digest);
 
     static IntegrityParseResult parseIntegrityAttribute(const WTF::String& attribute, WTF::Vector<IntegrityMetadata>& metadataList, Document&);
 };
 
 } // namespace blink
 
 #endif