Ensure BrowserThread::CurrentlyOn is correct through MessageLoop teardown

content/browser/browser_thread_impl.h

Index: content/browser/browser_thread_impl.h
diff --git a/content/browser/browser_thread_impl.h b/content/browser/browser_thread_impl.h
index dfb5da4a600f4489e9d65648190128922e61d332..e86f4ec907a76f9fe3aab439db527f4d94f94935 100644
--- a/content/browser/browser_thread_impl.h
+++ b/content/browser/browser_thread_impl.h
@@ -5,6 +5,7 @@
 #ifndef CONTENT_BROWSER_BROWSER_THREAD_IMPL_H_
 #define CONTENT_BROWSER_BROWSER_THREAD_IMPL_H_
 
+#include "base/threading/platform_thread.h"
 #include "base/threading/thread.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/browser_thread.h"
@@ -25,7 +26,9 @@ class CONTENT_EXPORT BrowserThreadImpl : public BrowserThread,
                     base::MessageLoop* message_loop);
   ~BrowserThreadImpl() override;
 
+  bool Start();
   bool StartWithOptions(const Options& options);
+  bool StartAndWaitForTesting();
 
   static void ShutdownThreadPool();