Add SpdyString alias for std::string in net/spdy.

net/spdy/spdy_header_indexing.h

 // Copyright (c) 2016 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.
 
 #ifndef NET_SPDY_SPDY_HEADER_INDEXING_H_
 #define NET_SPDY_SPDY_HEADER_INDEXING_H_
 
 #include <stdint.h>
 #include <memory>
-#include <string>
 #include <unordered_set>
 #include <utility>
 
 #include "net/base/net_export.h"
+#include "net/spdy/platform/api/spdy_string.h"
 #include "net/spdy/platform/api/spdy_string_piece.h"
 
 namespace net {
 
 namespace test {
 class HeaderIndexingPeer;
 }
 
 NET_EXPORT_PRIVATE extern int32_t FLAGS_gfe_spdy_indexing_set_bound;
 NET_EXPORT_PRIVATE extern int32_t FLAGS_gfe_spdy_tracking_set_bound;
 
 // Maintain two headers sets: Indexing set and tracking
 // set. Call ShouldIndex() for each header to decide if to index it. If for some
 // connections, we decide to index all headers, we may still want to call
 // UpdateSets to log the headers into both sets.
 class NET_EXPORT HeaderIndexing {
  public:
-  using HeaderSet = std::unordered_set<std::string>;
+  using HeaderSet = std::unordered_set<SpdyString>;
 
   HeaderIndexing();
   ~HeaderIndexing();
 
   void CreateInitIndexingHeaders();
 
   // Decide if a header should be indexed. We only use |header|. Add |value| to
   // be consistent with HPACK indexing policy interface.
   bool ShouldIndex(SpdyStringPiece header, SpdyStringPiece value);
 
   // Not to make the indexing decision but to update sets.
   void UpdateSets(SpdyStringPiece header, SpdyStringPiece value) {
     update_only_header_count_++;
     ShouldIndex(header, value);
   }
 
   int64_t total_header_count() { return total_header_count_; }
   int64_t update_only_header_count() { return update_only_header_count_; }
   int64_t missed_headers_in_indexing() { return missed_header_in_indexing_; }
   int64_t missed_headers_in_tracking() { return missed_header_in_tracking_; }
 
  private:
   friend class test::HeaderIndexingPeer;
-  void TryInsertHeader(std::string&& header, HeaderSet* set, size_t bound);
+  void TryInsertHeader(SpdyString&& header, HeaderSet* set, size_t bound);
   // Headers to index.
   HeaderSet indexing_set_;
   // Headers seen so far.
   HeaderSet tracking_set_;
   const size_t indexing_set_bound_;
   const size_t tracking_set_bound_;
   int64_t total_header_count_ = 0;
   int64_t update_only_header_count_ = 0;
   int64_t missed_header_in_indexing_ = 0;
   int64_t missed_header_in_tracking_ = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_SPDY_SPDY_HEADER_INDEXING_H_