Use a better method to generate a random ID in IvfFileWriterTest.

webrtc/modules/video_coding/utility/ivf_file_writer_unittest.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include "webrtc/modules/video_coding/utility/ivf_file_writer.h"
 
 #include <memory>
 
 #include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/base/helpers.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/thread.h"
 #include "webrtc/base/timeutils.h"
 #include "webrtc/modules/rtp_rtcp/source/byte_io.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
 namespace {
 static const int kHeaderSize = 32;
 static const int kFrameHeaderSize = 12;
 static uint8_t dummy_payload[4] = {0, 1, 2, 3};
 static const int kMaxFileRetries = 5;
 }  // namespace
 
 class IvfFileWriterTest : public ::testing::Test {
  protected:
   void SetUp() override {
-    const int64_t start_id =
-        reinterpret_cast<int64_t>(this) ^ rtc::TimeMicros();
-    int64_t id = start_id;
+    const uint64_t start_id = rtc::CreateRandomId64();
+    uint64_t id = start_id;
     do {
       std::ostringstream oss;
       oss << test::OutputPath() << "ivf_test_file_" << id++ << ".ivf";
       file_name_ = oss.str();
-    } while (id < start_id + 100 && FileExists(false));
-    ASSERT_LT(id, start_id + 100);
+    } while ((id - start_id) < 100u && FileExists(false));
+    ASSERT_LT(id - start_id, 100u);
   }
 
   bool WriteDummyTestFrames(int width,
                             int height,
                             int num_frames,
                             bool use_capture_tims_ms) {
     EncodedImage frame;
     frame._buffer = dummy_payload;
     frame._encodedWidth = width;
     frame._encodedHeight = height;
@@ skipping 141 matching lines @@
   const uint8_t fourcc[4] = {'H', '2', '6', '4'};
   RunBasicFileStructureTest(kVideoCodecH264, fourcc, false);
 }
 
 TEST_F(IvfFileWriterTest, WritesBasicH264FileMsTimestamp) {
   const uint8_t fourcc[4] = {'H', '2', '6', '4'};
   RunBasicFileStructureTest(kVideoCodecH264, fourcc, true);
 }
 
 }  // namespace webrtc