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

content/child/webcrypto/test/aes_gcm_unittest.cc

Index: content/child/webcrypto/test/aes_gcm_unittest.cc
diff --git a/content/child/webcrypto/test/aes_gcm_unittest.cc b/content/child/webcrypto/test/aes_gcm_unittest.cc
index 8f4b910f9b10b04915db643ad6e33894c5cdfc90..8825741379874eac29801c0d94b1541453d1a9ed 100644
--- a/content/child/webcrypto/test/aes_gcm_unittest.cc
+++ b/content/child/webcrypto/test/aes_gcm_unittest.cc
@@ -109,7 +109,7 @@ TEST(WebCryptoAesGcmTest, GenerateKeyBadLength) {
   }
 
   const unsigned short kKeyLen[] = {0, 127, 257};
-  blink::WebCryptoKey key = blink::WebCryptoKey::createNull();
+  blink::WebCryptoKey key;
   for (size_t i = 0; i < arraysize(kKeyLen); ++i) {
     SCOPED_TRACE(i);
     EXPECT_EQ(Status::ErrorGenerateKeyLength(),