Add a new QuicFlagSaver class for saving/restoring the values of QUIC flags in tests.

net/quic/core/quic_stream_sequencer_buffer_test.cc

 // Copyright (c) 2015 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/quic/core/quic_stream_sequencer_buffer.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <string>
 #include <utility>
@@ skipping 816 matching lines @@
   EXPECT_EQ(max_capacity_bytes_ + 512, buffer_->BytesConsumed());
   EXPECT_TRUE(buffer_->Empty());
   EXPECT_TRUE(helper_->CheckBufferInvariants());
   // Clear buffer at this point should still preserve BytesConsumed().
   buffer_->Clear();
   EXPECT_EQ(max_capacity_bytes_ + 512, buffer_->BytesConsumed());
   EXPECT_TRUE(helper_->CheckBufferInvariants());
 }
 
 TEST_F(QuicStreamSequencerBufferTest, TooManyGaps) {
+  QuicFlagSaver flags;
   FLAGS_quic_limit_frame_gaps_in_buffer = true;
   // Make sure max capacity is large enough that it is possible to have more
   // than |kMaxNumGapsAllowed| number of gaps.
   max_capacity_bytes_ = 3 * kBlockSizeBytes;
   // Feed buffer with 1-byte discontiguous frames. e.g. [1,2), [3,4), [5,6)...
   for (QuicStreamOffset begin = 1; begin <= max_capacity_bytes_; begin += 2) {
     size_t written;
     QuicErrorCode rs = buffer_->OnStreamData(
         begin, "a", clock_.ApproximateNow(), &written, &error_details_);
 
@@ skipping 230 matching lines @@
   EXPECT_LE(bytes_to_buffer_, total_bytes_read_) << "iterations: "
                                                  << iterations;
   EXPECT_LE(bytes_to_buffer_, total_bytes_written_);
 }
 
 }  // anonymous namespace
 
 }  // namespace test
 
 }  // namespace net