Avoid SpdyHeaderBlock copy in SpdyStream::OnPushPromiseHeadersReceived().

net/spdy/header_coalescer.cc

 // 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.
 
 #include "net/spdy/header_coalescer.h"
 
+#include <utility>
+
 #include "base/strings/string_util.h"
 
 namespace net {
 
 const size_t kMaxHeaderListSize = 256 * 1024;
 
 void HeaderCoalescer::OnHeader(base::StringPiece key, base::StringPiece value) {
   if (error_seen_) {
     return;
   }
@@ skipping 31 matching lines @@
       // Obeys section 8.1.2.5 in RFC 7540 for cookie reconstruction.
       s.append("; ");
     } else {
       base::StringPiece("\0", 1).AppendToString(&s);
     }
     value.AppendToString(&s);
     headers_.ReplaceOrAppendHeader(key, s);
   }
 }
 
+SpdyHeaderBlock HeaderCoalescer::release_headers() {
+  DCHECK(headers_valid_);
+  headers_valid_ = false;
+  return std::move(headers_);
+}
+
 }  // namespace net