[webcrypto] Remove the TODO for NullKey().

content/renderer/webcrypto/webcrypto_impl_unittest.cc

Index: content/renderer/webcrypto/webcrypto_impl_unittest.cc
diff --git a/content/renderer/webcrypto/webcrypto_impl_unittest.cc b/content/renderer/webcrypto/webcrypto_impl_unittest.cc
index 503bdb8c9ffaf327bab4413ecc43091a06872360..784da6ba52b764113486169f24fff36b5a073e8e 100644
--- a/content/renderer/webcrypto/webcrypto_impl_unittest.cc
+++ b/content/renderer/webcrypto/webcrypto_impl_unittest.cc
@@ -114,6 +114,7 @@ class WebCryptoImplTest : public testing::Test {
                                           &key));
 
     EXPECT_EQ(WebKit::WebCryptoKeyTypeSecret, key.type());
+    EXPECT_FALSE(key.isNull());
     EXPECT_TRUE(key.handle());
     return key;
   }
@@ -658,6 +659,7 @@ TEST_F(WebCryptoImplTest, GenerateKeyHmac) {
   WebKit::WebCryptoAlgorithm algorithm =
       CreateHmacKeyAlgorithm(WebKit::WebCryptoAlgorithmIdSha1, 128);
   ASSERT_TRUE(GenerateKeyInternal(algorithm, &key));
+  EXPECT_FALSE(key.isNull());
   EXPECT_TRUE(key.handle());
   EXPECT_EQ(WebKit::WebCryptoKeyTypeSecret, key.type());
 }