Fix compile issue of jpeg decoder unit tests

content/common/gpu/media/vaapi_jpeg_decoder_unittest.cc

 // Copyright 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 <string>
 
 // This has to be included first.
 // See http://code.google.com/p/googletest/issues/detail?id=371
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ skipping 28 matching lines @@
     wrapper_ = VaapiWrapper::Create(VaapiWrapper::kDecode,
                                     VAProfileJPEGBaseline, report_error_cb);
     ASSERT_TRUE(wrapper_);
 
     base::FilePath input_file = media::GetTestDataFilePath(kTestFilename);
 
     ASSERT_TRUE(base::ReadFileToString(input_file, &jpeg_data_))
         << "failed to read input data from " << input_file.value();
   }
 
-  void TearDown() override { wrapper_.reset(); }
+  void TearDown() override { wrapper_ = nullptr; }
 
   bool VerifyDecode(const media::JpegParseResult& parse_result,
                     const std::string& md5sum);
 
  protected:
   scoped_refptr<VaapiWrapper> wrapper_;
   std::string jpeg_data_;
 };
 
 bool VaapiJpegDecoderTest::VerifyDecode(
@@ skipping 69 matching lines @@
 
 }  // namespace
 }  // namespace content
 
 int main(int argc, char** argv) {
   testing::InitGoogleTest(&argc, argv);
   base::AtExitManager exit_manager;
   content::VaapiWrapper::PreSandboxInitialization();
   return RUN_ALL_TESTS();
 }