Fix some includes in //net/http2/.

net/http2/hpack/decoder/hpack_decoder_string_buffer_test.cc

 // Copyright 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/http2/hpack/decoder/hpack_decoder_string_buffer.h"
 
 // Tests of HpackDecoderStringBuffer.
 
-#include <initializer_list>
 #include <sstream>
 #include <string>
 
 #include "base/logging.h"
 #include "base/strings/string_piece.h"
 #include "net/http2/tools/failure.h"
 #include "net/spdy/spdy_test_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ skipping 216 matching lines @@
   EXPECT_EQ(state(), State::COLLECTING);
   EXPECT_EQ(backing(), Backing::BUFFERED);
 
   EXPECT_FALSE(buf_.OnEnd());
   LOG(INFO) << buf_;
 }
 
 }  // namespace
 }  // namespace test
 }  // namespace net