Cleanup: Use default constructor for WebCryptoKey rather than createNull() factory method.

content/child/webcrypto/test/test_helpers.cc

Index: content/child/webcrypto/test/test_helpers.cc
diff --git a/content/child/webcrypto/test/test_helpers.cc b/content/child/webcrypto/test/test_helpers.cc
index ddabd7574c459a881144d253ad7ffed26e1c41d8..e65a23d9445bd59445fa459bc0bb62f110f998f1 100644
--- a/content/child/webcrypto/test/test_helpers.cc
+++ b/content/child/webcrypto/test/test_helpers.cc
@@ -75,7 +75,7 @@ bool operator!=(const CryptoData& a, const CryptoData& b) {
 bool SupportsAesGcm() {
   std::vector<uint8_t> key_raw(16, 0);
 
-  blink::WebCryptoKey key = blink::WebCryptoKey::createNull();
+  blink::WebCryptoKey key;
   Status status = ImportKey(blink::WebCryptoKeyFormatRaw,
                             CryptoData(key_raw),
                             CreateAlgorithm(blink::WebCryptoAlgorithmIdAesGcm),
@@ -326,7 +326,7 @@ blink::WebCryptoKey ImportSecretKeyFromRaw(
     const std::vector<uint8_t>& key_raw,
     const blink::WebCryptoAlgorithm& algorithm,
     blink::WebCryptoKeyUsageMask usage) {
-  blink::WebCryptoKey key = blink::WebCryptoKey::createNull();
+  blink::WebCryptoKey key;
   bool extractable = true;
   EXPECT_EQ(Status::Success(),
             ImportKey(blink::WebCryptoKeyFormatRaw,