[Fetch API] Implement combining of Headers with same keys.

third_party/WebKit/Source/modules/fetch/FetchHeaderList.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/fetch/FetchHeaderList.h"
 
 #include "core/fetch/FetchUtils.h"
 #include "platform/network/HTTPParsers.h"
 #include "wtf/PtrUtil.h"
 #include <algorithm>
@@ skipping 112 matching lines @@
     if (!FetchUtils::isSimpleHeader(AtomicString(m_headerList[i]->first),
                                     AtomicString(m_headerList[i]->second)))
       return true;
   }
   return false;
 }
 
 void FetchHeaderList::sortAndCombine() {
   // https://fetch.spec.whatwg.org/#concept-header-list-sort-and-combine
   // "To sort and combine a header list..."
-
-  // TODO(jsbell): Implement the combining part - this currently just sorts.
+  if (m_headerList.isEmpty())
+    return;
 
   std::sort(
       m_headerList.begin(), m_headerList.end(),
       [](const std::unique_ptr<Header>& a, const std::unique_ptr<Header>& b) {
         return WTF::codePointCompareLessThan(a->first, b->first);
       });
+
+  for (size_t index = m_headerList.size() - 1; index > 0; --index) {
+    if (m_headerList[index - 1]->first == m_headerList[index]->first) {
+      m_headerList[index - 1]->second.append(",");
+      m_headerList[index - 1]->second.append(m_headerList[index]->second);
+      m_headerList.remove(index, 1);
+    }
+  }
 }
 
 bool FetchHeaderList::isValidHeaderName(const String& name) {
   // "A name is a case-insensitive byte sequence that matches the field-name
   // token production."
   return isValidHTTPToken(name);
 }
 
 bool FetchHeaderList::isValidHeaderValue(const String& value) {
   // "A value is a byte sequence that matches the field-value token production
   // and contains no 0x0A or 0x0D bytes."
   return isValidHTTPHeaderValue(value);
 }
 
 }  // namespace blink