[CrOS MultiDevice] Add FakeTimerFactory::num_instances_created().

Bug: 824568, 752273
Change-Id: I7bafac91260e56b977caf89738931ad752115b73
Reviewed-on: https://chromium-review.googlesource.com/1093383Reviewed-by: Jeremy Klein <jlklein@chromium.org>
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565704}

chromeos/services/secure_channel/fake_timer_factory.cc

@@ -17,6 +17,8 @@ FakeTimerFactory::FakeTimerFactory() : weak_ptr_factory_(this) {}
 FakeTimerFactory::~FakeTimerFactory() = default;
 
 std::unique_ptr<base::Timer> FakeTimerFactory::CreateOneShotTimer() {
+  ++num_instances_created_;
+
   auto fake_one_shot_timer = std::make_unique<FakeOneShotTimer>(
       base::BindOnce(&FakeTimerFactory::OnOneShotTimerDeleted,
                      weak_ptr_factory_.GetWeakPtr()));

chromeos/services/secure_channel/fake_timer_factory.h

@@ -34,6 +34,8 @@ class FakeTimerFactory : public TimerFactory {
     return id_to_active_one_shot_timer_map_;
   }
 
+  size_t num_instances_created() const { return num_instances_created_; }
+
  private:
   // TimerFactory:
   std::unique_ptr<base::Timer> CreateOneShotTimer() override;
@@ -43,6 +45,7 @@ class FakeTimerFactory : public TimerFactory {
   base::UnguessableToken id_for_last_created_one_shot_timer_;
   base::flat_map<base::UnguessableToken, FakeOneShotTimer*>
       id_to_active_one_shot_timer_map_;
+  size_t num_instances_created_ = 0u;
 
   base::WeakPtrFactory<FakeTimerFactory> weak_ptr_factory_;