Improve usage documentation of scoped task environments.

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, a blocking pool, and a task scheduler in unit tests. For
 // most tests, it is sufficient to just instantiate the TestBrowserThreadBundle
 // as a member variable. It is a good idea to put the TestBrowserThreadBundle as
 // the first member variable in test classes, so it is destroyed last, and the
 // test threads always exist from the perspective of other classes.
@@ skipping 35 matching lines @@
 // IO_MAINLOOP option. Most of the time, IO_MAINLOOP avoids needing to use a
 // REAL_IO_THREAD.
 //
 // For some tests it is important to emulate real browser startup. During real
 // browser startup, the main MessageLoop is created before other threads.
 // Passing DONT_CREATE_THREADS to constructor will delay creating other threads
 // until the test explicitly calls CreateThreads().
 //
 // DONT_CREATE_THREADS should only be used when the options specify at least
 // one real thread other than the main thread.
+//
+// Basic usage:
+//
+//   class MyTestFixture : public testing::Test {
+//    public:
+//     (...)
+//
+//    protected:
+//     // Must be first member (or at least before any member that cares about
+//     // tasks) to be initialized first and destroyed last. protected instead
+//     // of private visibility will allow controlling the task environment
+//     // (e.g. clock) once such features are added (see
+//     // base::test::ScopedTaskEnvironment for details), until then it at least
+//     // doesn't hurt :).
+//     content::TestBrowserThreadBundle test_browser_thread_bundle_;
+//
+//     // Other members go here (or further below in private section.)
+//   };
 
 #ifndef CONTENT_PUBLIC_TEST_TEST_BROWSER_THREAD_BUNDLE_H_
 #define CONTENT_PUBLIC_TEST_TEST_BROWSER_THREAD_BUNDLE_H_
 
 #include <memory>
 
 #include "base/macros.h"
 
 namespace base {
 class MessageLoop;
@@ skipping 45 matching lines @@
 
   int options_;
   bool threads_created_;
 
   DISALLOW_COPY_AND_ASSIGN(TestBrowserThreadBundle);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_TEST_TEST_BROWSER_THREAD_BUNDLE_H_