[ServiceWorker] Make Response class better conformance with the spec.

Source/modules/serviceworkers/ResponseInit.h

Index: Source/modules/serviceworkers/ResponseInit.h
diff --git a/Source/modules/serviceworkers/ResponseInit.h b/Source/modules/serviceworkers/ResponseInit.h
index bda31bd5aa5efa060d908307e065a9ca6b326fbe..7cef14212341bbc2644567b4dc15f678ddb9664c 100644
--- a/Source/modules/serviceworkers/ResponseInit.h
+++ b/Source/modules/serviceworkers/ResponseInit.h
@@ -6,7 +6,7 @@
 #define ResponseInit_h
 
 #include "bindings/core/v8/Dictionary.h"
-#include "modules/serviceworkers/HeaderMap.h"
+#include "modules/serviceworkers/Headers.h"
 #include "wtf/RefPtr.h"
 
 namespace WebCore {
@@ -25,11 +25,15 @@ struct ResponseInit {
         // FIXME: Spec uses ByteString for statusText. http://crbug.com/347426
         options.get("statusText", statusText);
         options.get("headers", headers);
+        if (!headers) {
+            options.get("headers", headersDictionary);
+        }
     }
 
     unsigned short status;
     String statusText;
-    RefPtr<HeaderMap> headers;
+    RefPtr<Headers> headers;
+    Dictionary headersDictionary;
 };
 
 }