Revert of Avoids the "re-encode HPACK as SPDY3" step.

net/spdy/header_coalescer.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_HEADER_COALESCER_H_
-#define NET_SPDY_HEADER_COALESCER_H_
-
-#include "net/base/net_export.h"
-#include "net/spdy/spdy_header_block.h"
-#include "net/spdy/spdy_headers_handler_interface.h"
-
-namespace net {
-
-class NET_EXPORT_PRIVATE HeaderCoalescer : public SpdyHeadersHandlerInterface {
- public:
-  HeaderCoalescer() {}
-
-  void OnHeaderBlockStart() override {}
-
-  void OnHeader(base::StringPiece key, base::StringPiece value) override;
-
-  void OnHeaderBlockEnd(size_t uncompressed_header_bytes) override {}
-
-  const SpdyHeaderBlock& headers() const { return headers_; }
-  bool error_seen() const { return error_seen_; }
-
- private:
-  SpdyHeaderBlock headers_;
-  bool error_seen_ = false;
-};
-
-}  // namespace net
-
-#endif  // NET_SPDY_HEADER_COALESCER_H_