Add an Error class for ServiceWorkers

public/platform/WebServiceWorkerError.h

Index: public/platform/WebServiceWorkerError.h
diff --git a/public/platform/WebMIDIAccessor.h b/public/platform/WebServiceWorkerError.h
similarity index 81%
copy from public/platform/WebMIDIAccessor.h
copy to public/platform/WebServiceWorkerError.h
index 71aba260a77ed58e7eb6d168429628430aafd97c..8ae4c2791e32e4d0a7debad45fd18743ee111b5f 100644
--- a/public/platform/WebMIDIAccessor.h
+++ b/public/platform/WebServiceWorkerError.h
@@ -28,22 +28,26 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef WebMIDIAccessor_h
-#define WebMIDIAccessor_h
+#ifndef WebServiceWorkerError_h
+#define WebServiceWorkerError_h
 
 #include "WebString.h"
 
 namespace WebKit {
 
-class WebMIDIAccessor {
-public:
-    virtual ~WebMIDIAccessor() { }
+struct WebServiceWorkerError {
+    enum ErrorType {
+        DisabledError = 0,
+        SecurityError
+    };
 
-    virtual void startSession() { }
-    // |timeStamp| is measured in milliseconds as Web MIDI spec defines.
-    virtual void sendMIDIData(unsigned portIndex, const unsigned char* data, size_t length, double timeStamp) { }
+    WebServiceWorkerError(ErrorType errorType, const WebString& message)
+        : errorType(errorType), message(message) { }
+
+    ErrorType errorType;
+    WebString message;
 };
 
 } // namespace WebKit
 
-#endif // WebMIDIAccessor_h
+#endif