Support for the new WebCrypto digest by chunks API.

content/child/webcrypto/shared_crypto.cc

Index: content/child/webcrypto/shared_crypto.cc
diff --git a/content/child/webcrypto/shared_crypto.cc b/content/child/webcrypto/shared_crypto.cc
index af2beaca2a672fbbca28886ed65115dfb49e5112..ad8ea0453e5015772e1e02d5e6e685b04796039f 100644
--- a/content/child/webcrypto/shared_crypto.cc
+++ b/content/child/webcrypto/shared_crypto.cc
@@ -519,6 +519,11 @@ Status Digest(const blink::WebCryptoAlgorithm& algorithm,
   }
 }
 
+scoped_ptr<blink::WebCryptoDigestor> CreateDigestor(
+    blink::WebCryptoAlgorithmId algorithm) {
+  return platform::CreateDigestor(algorithm);
+}
+
 Status GenerateSecretKey(const blink::WebCryptoAlgorithm& algorithm,
                          bool extractable,
                          blink::WebCryptoKeyUsageMask usage_mask,