[ServiceWorker] Make fetch() method better conformance with the spec.

Source/modules/serviceworkers/FetchHeaderList.h

Index: Source/modules/serviceworkers/FetchHeaderList.h
diff --git a/Source/modules/serviceworkers/FetchHeaderList.h b/Source/modules/serviceworkers/FetchHeaderList.h
index 25711862ca96dfbcb84d6400175b02fcf5c94b64..e1806839ab57b4367a455422e5a727ef1ea64450 100644
--- a/Source/modules/serviceworkers/FetchHeaderList.h
+++ b/Source/modules/serviceworkers/FetchHeaderList.h
@@ -37,6 +37,8 @@ public:
     bool has(const String&) const;
     void clearList();
 
+    bool containsNonSimpleHeader() const;
+
     const Vector<OwnPtr<Header> >& list() const { return m_headerList; }
 
     static bool isValidHeaderName(const String&);