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

Source/modules/serviceworkers/FetchHeaderList.cpp

Index: Source/modules/serviceworkers/FetchHeaderList.cpp
diff --git a/Source/modules/serviceworkers/FetchHeaderList.cpp b/Source/modules/serviceworkers/FetchHeaderList.cpp
index 5eddc105521018c6ffd4bded6567575159c8256c..0a8bee219ddef643f2c4e73f066a961f9436b690 100644
--- a/Source/modules/serviceworkers/FetchHeaderList.cpp
+++ b/Source/modules/serviceworkers/FetchHeaderList.cpp
@@ -121,6 +121,15 @@ void FetchHeaderList::clearList()
     m_headerList.clear();
 }
 
+bool FetchHeaderList::containsNonSimpleHeader() const
+{
+    for (size_t i = 0; i < m_headerList.size(); ++i) {
+        if (!isSimpleHeader(m_headerList[i]->first, m_headerList[i]->second))
+            return true;
+    }
+    return false;
+}
+
 bool FetchHeaderList::isValidHeaderName(const String& name)
 {
     // "A name is a case-insensitive byte sequence that matches the field-name