Use the ToV8() overload that takes ScriptState for CryptoKey.

Bug: 740871
Change-Id: Ica5bcd76a3f2995a8f414c80698e468f8780734c
Reviewed-on: https://chromium-review.googlesource.com/568595Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486200}

third_party/WebKit/Source/modules/crypto/CryptoKey.cpp

@@ -162,9 +162,7 @@ ScriptValue CryptoKey::usages(ScriptState* script_state) {
       result.push_back(KeyUsageToString(usage));
   }
 
-  return ScriptValue(script_state,
-                     ToV8(result, script_state->GetContext()->Global(),
-                          script_state->GetIsolate()));
+  return ScriptValue(script_state, ToV8(result, script_state));
 }
 
 bool CryptoKey::CanBeUsedForAlgorithm(const WebCryptoAlgorithm& algorithm,