TaskScheduler: Add FlushForTesting().

base/task_scheduler/task_tracker.h

Index: base/task_scheduler/task_tracker.h
diff --git a/base/task_scheduler/task_tracker.h b/base/task_scheduler/task_tracker.h
index 7a4338943341e25609987d8ec61b415514761e5c..93769f1751bc1525c8c1cf13cf19b271ea6b1567 100644
--- a/base/task_scheduler/task_tracker.h
+++ b/base/task_scheduler/task_tracker.h
@@ -7,6 +7,7 @@
 
 #include <memory>
 
+#include "base/atomicops.h"
 #include "base/base_export.h"
 #include "base/callback_forward.h"
 #include "base/macros.h"
@@ -19,6 +20,7 @@
 
 namespace base {
 
+class ConditionVariable;
 class SequenceToken;
 
 namespace internal {
@@ -40,6 +42,13 @@ class BASE_EXPORT TaskTracker {
   // This can only be called once.
   void Shutdown();
 
+  // Waits until there are no pending undelayed tasks. May be called in tests
+  // to validate that a condition is met after all undelayed tasks have run.
+  //
+  // Does not wait for delayed tasks. Waits for undelayed tasks posted from
+  // other threads during the call. Returns immediately when shutdown completes.
+  void Flush();
+
   // Informs this TaskTracker that |task| is about to be posted. Returns true if
   // this operation is allowed (|task| should be posted if-and-only-if it is).
   bool WillPostTask(const Task* task);
@@ -67,6 +76,8 @@ class BASE_EXPORT TaskTracker {
  private:
   class State;
 
+  void PerformShutdown();
+
   // Called before WillPostTask() informs the tracing system that a task has
   // been posted. Updates |num_tasks_blocking_shutdown_| if necessary and
   // returns true if the current shutdown state allows the task to be posted.
@@ -86,10 +97,30 @@ class BASE_EXPORT TaskTracker {
   // shutdown has started.
   void OnBlockingShutdownTasksComplete();
 
+  // Decrements the number of pending undelayed tasks and signals |flush_cv_| if
+  // it reaches zero.
+  void DecrementNumPendingUndelayedTasks();
+
   // Number of tasks blocking shutdown and boolean indicating whether shutdown
   // has started.
   const std::unique_ptr<State> state_;
 
+  // Number of undelayed tasks that haven't completed their execution. Is
+  // incremented and decremented without a barrier. When it reaches zero,
+  // |flush_lock_| is acquired (forcing memory synchronization) and |flush_cv_|
+  // is signaled.
+  subtle::Atomic32 num_pending_undelayed_tasks_ = 0;
+
+  // Lock associated with |flush_cv_|. Partially synchronizes access to
+  // |num_pending_undelayed_tasks_|. Full synchronization isn't needed because
+  // it's atomic, but synchronization is needed to coordinate waking and
+  // sleeping at the right time.
+  mutable SchedulerLock flush_lock_;
+
+  // Signaled when |num_pending_undelayed_tasks_| is zero or when shutdown
+  // completes.
+  const std::unique_ptr<ConditionVariable> flush_cv_;
+
   // Synchronizes access to shutdown related members below.
   mutable SchedulerLock shutdown_lock_;