Use std::unique_ptr to pass around WebCryptoDigestor.

components/webcrypto/webcrypto_impl.h

Index: components/webcrypto/webcrypto_impl.h
diff --git a/components/webcrypto/webcrypto_impl.h b/components/webcrypto/webcrypto_impl.h
index af5f6fcc3563c27cbff6ea88fce82e366b8346f1..b551213351ff01d4440f8d17cf6569a1f810f968 100644
--- a/components/webcrypto/webcrypto_impl.h
+++ b/components/webcrypto/webcrypto_impl.h
@@ -96,10 +96,8 @@ class WebCryptoImpl : public blink::WebCrypto {
   // This method returns a digestor object that can be used to synchronously
   // compute a digest one chunk at a time. Thus, the consume does not need to
   // hold onto a large buffer with all the data to digest. Chunks can be given
-  // one at a time and the digest will be computed piecemeal. The allocated
-  // WebCrytpoDigestor that is returned by createDigestor must be freed by the
-  // caller.
-  blink::WebCryptoDigestor* createDigestor(
+  // one at a time and the digest will be computed piecemeal.
+  std::unique_ptr<blink::WebCryptoDigestor> createDigestor(
       blink::WebCryptoAlgorithmId algorithm_id) override;
 
   bool deserializeKeyForClone(const blink::WebCryptoKeyAlgorithm& algorithm,