Update from https://crrev.com/316786

sandbox/linux/services/thread_helpers.h

Index: sandbox/linux/services/thread_helpers.h
diff --git a/sandbox/linux/services/thread_helpers.h b/sandbox/linux/services/thread_helpers.h
index 377742a539acd4abb169ca400c0dcfabc3a74c37..efc24589224e4989f2b1a4bc0cebc0ae4183c053 100644
--- a/sandbox/linux/services/thread_helpers.h
+++ b/sandbox/linux/services/thread_helpers.h
@@ -15,18 +15,26 @@ namespace sandbox {
 class SANDBOX_EXPORT ThreadHelpers {
  public:
   // Check whether the current process is single threaded. |proc_self_tasks|
-  // can be a file descriptor to /proc/self/task/ and remains owned by the
-  // caller or -1.
-  // If |proc_self_tasks| is -1, this method will open /proc/self/task/ and
-  // crash if it cannot.
+  // must be a file descriptor to /proc/self/task/ and remains owned by the
+  // caller.
   static bool IsSingleThreaded(int proc_self_task);
+  static bool IsSingleThreaded();
+
+  // Crash if the current process is not single threaded. This will wait
+  // on /proc to be updated. In the case where this doesn't crash, this will
+  // return promptly. In the case where this does crash, this will first wait
+  // for a few ms in Debug mode, a few seconds in Release mode.
+  static void AssertSingleThreaded(int proc_self_task);
+  static void AssertSingleThreaded();
 
   // Stop |thread| and ensure that it does not have an entry in
   // /proc/self/task/ from the point of view of the current thread. This is
   // the way to stop threads before calling IsSingleThreaded().
-  static bool StopThreadAndWatchProcFS(int proc_self_tasks,
+  static bool StopThreadAndWatchProcFS(int proc_self_task,
                                        base::Thread* thread);
 
+  static const char* GetAssertSingleThreadedErrorMessageForTests();
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ThreadHelpers);
 };