Flush the blocking pool in TestBrowserThreadBundle.

content/public/test/test_browser_thread_bundle.h

 // Copyright 2013 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.
 
 // TestBrowserThreadBundle is a convenience class for creating a set of
 // TestBrowserThreads in unit tests.  For most tests, it is sufficient to
 // just instantiate the TestBrowserThreadBundle as a member variable.
 //
 // By default, all of the created TestBrowserThreads will be backed by a single
 // shared MessageLoop. If a test truly needs separate threads, it can do
 // so by passing the appropriate combination of RealThreadsMask values during
 // the TestBrowserThreadBundle construction.
 //
 // The TestBrowserThreadBundle will attempt to drain the MessageLoop on
 // destruction. Sometimes a test needs to drain currently enqueued tasks
 // mid-test. Browser tests should call content::RunAllPendingInMessageLoop().
 // Unit tests should use base::RunLoop (e.g., base::RunLoop().RunUntilIdle()).
 // TODO(phajdan.jr): Revise this comment after switch to Aura.
 //
+// The TestBrowserThreadBundle will also flush the blocking pool on destruction.
+// We do this to avoid memory leaks, particularly in the case of threads posting
+// tasks to the blocking pool via PostTaskAndReply. By ensuring that the tasks
+// are run while the originating TestBroswserThreads still exist, we prevent
+// leakage of PostTaskAndReplyRelay objects. We also flush the blocking pool
+// again at the point where it would normally be shut down, to better simulate
+// the normal thread shutdown process.
+//
 // Some tests using the IO thread expect a MessageLoopForIO. Passing
 // IO_MAINLOOP will use a MessageLoopForIO for the main MessageLoop.
 // Most of the time, this avoids needing to use a REAL_IO_THREAD.
 
 #ifndef CONTENT_PUBLIC_TEST_TEST_BROWSER_THREAD_TEST_BUNDLE_H_
 #define CONTENT_PUBLIC_TEST_TEST_BROWSER_THREAD_TEST_BUNDLE_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ skipping 37 matching lines @@
   scoped_ptr<TestBrowserThread> process_launcher_thread_;
   scoped_ptr<TestBrowserThread> cache_thread_;
   scoped_ptr<TestBrowserThread> io_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(TestBrowserThreadBundle);
 };
 
 }  // namespace content
 
 #endif /* CONTENT_PUBLIC_TEST_TEST_BROWSER_THREAD_TEST_BUNDLE_H_ */