Experiment with redirecting all BrowserThreads (but UI/IO) to TaskScheduler

content/browser/browser_thread_impl.h

 // 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.
 
 #ifndef CONTENT_BROWSER_BROWSER_THREAD_IMPL_H_
 #define CONTENT_BROWSER_BROWSER_THREAD_IMPL_H_
 
-#include "base/threading/platform_thread.h"
+#include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
 #include "base/threading/thread.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace content {
 
 class CONTENT_EXPORT BrowserThreadImpl : public BrowserThread,
                                          public base::Thread {
  public:
   // Construct a BrowserThreadImpl with the supplied identifier.  It is an error
   // to construct a BrowserThreadImpl that already exists.
   explicit BrowserThreadImpl(BrowserThread::ID identifier);
 
   // Special constructor for the main (UI) thread and unittests. If a
   // |message_loop| is provied, we use a dummy thread here since the main
   // thread already exists.
   BrowserThreadImpl(BrowserThread::ID identifier,
                     base::MessageLoop* message_loop);
   ~BrowserThreadImpl() override;
 
-  bool Start();
-  bool StartWithOptions(const Options& options);
-  bool StartAndWaitForTesting();
+  // Redirects tasks posted to |identifier| to |task_runner|. |task_runner| may
+  // be null to cancel the redirection and have |identifier| enter its
+  // "shutdown" phase.
+  static void RedirectThreadIDToTaskRunner(
+      BrowserThread::ID identifier,
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
 
   static void ShutdownThreadPool();
 
+  // Resets globals for |identifier|. Used in tests to clear global state that
+  // would otherwise leak to the next test. Globals are not otherwise fully
+  // cleaned up in ~BrowserThreadImpl() as there are subtle differences between
+  // UNINITIALIZED and SHUTDOWN state (e.g. globals.task_runners are kept around
+  // on shutdown). Must be called after ~BrowserThreadImpl() for the given
+  // |identifier|.
+  static void ResetGlobalsForTesting(BrowserThread::ID identifier);
+
  protected:
   void Init() override;
   void Run(base::RunLoop* run_loop) override;
   void CleanUp() override;
 
  private:
   // We implement all the functionality of the public BrowserThread
   // functions, but state is stored in the BrowserThreadImpl to keep
   // the API cleaner. Therefore make BrowserThread a friend class.
   friend class BrowserThread;
@@ skipping 24 matching lines @@
   static void FlushThreadPoolHelperForTesting();
 
   // The identifier of this thread.  Only one thread can exist with a given
   // identifier at a given time.
   ID identifier_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_BROWSER_THREAD_IMPL_H_