[webcrypto] Reject failed operations with a DOMException rather than null.

Source/platform/CryptoResult.h

Index: Source/platform/CryptoResult.h
diff --git a/Source/platform/CryptoResult.h b/Source/platform/CryptoResult.h
index 4c4e6d22a1b27a5090f103b3c8255b7abb580f58..af8032bc57997e4bd35febe1d797d841d1682a14 100644
--- a/Source/platform/CryptoResult.h
+++ b/Source/platform/CryptoResult.h
@@ -41,8 +41,7 @@ class CryptoResult : public ThreadSafeRefCounted<CryptoResult> {
 public:
     virtual ~CryptoResult() { }
 
-    virtual void completeWithError() = 0;
-    virtual void completeWithError(const blink::WebString&) = 0;
+    virtual void completeWithError(blink::WebCryptoErrorType, const blink::WebString&) = 0;
     virtual void completeWithBuffer(const blink::WebArrayBuffer&) = 0;
     virtual void completeWithBoolean(bool) = 0;
     virtual void completeWithKey(const blink::WebCryptoKey&) = 0;