Ensure that SequencedWorkerPools in tests don't outlive their tests

content/browser/trace_subscriber_stdio_unittest.cc

 // Copyright (c) 2012 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 "content/browser/trace_subscriber_stdio.h"
 
 #include "base/message_loop.h"
 #include "base/scoped_temp_dir.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "content/public/browser/browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-TEST(TraceSubscriberStdioTest, CanWriteDataToFile) {
+class TraceSubscriberStdioTest : public ::testing::Test {
+ private:
+  // Needed by the blocking pool (but no need to pump it).
+  MessageLoop message_loop_;
+};
+
+TEST_F(TraceSubscriberStdioTest, CanWriteDataToFile) {
   ScopedTempDir trace_dir;
   ASSERT_TRUE(trace_dir.CreateUniqueTempDir());
   FilePath trace_file(trace_dir.path().AppendASCII("trace.txt"));
   {
     content::TraceSubscriberStdio subscriber(trace_file);
 
     std::string foo("foo");
     subscriber.OnTraceDataCollected(
         make_scoped_refptr(base::RefCountedString::TakeString(&foo)));
 
     std::string bar("bar");
     subscriber.OnTraceDataCollected(
         make_scoped_refptr(base::RefCountedString::TakeString(&bar)));
 
     subscriber.OnEndTracingComplete();
   }
   content::BrowserThread::GetBlockingPool()->FlushForTesting();
   std::string result;
   EXPECT_TRUE(file_util::ReadFileToString(trace_file, &result));
   EXPECT_EQ("[foo,bar]", result);
 }