Hide deprecated SingleThreadedTaskQueueForTest behind an accessor

this change is intentionally noop.
Goal is to minimize change that would replace the
SingleThreadedTaskQueueForTest with a regular task queue.

Bug: webrtc:10933
Change-Id: I6da768941af048de3716af13e41b8f0f1ccd4cab
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157892
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29569}
diff --git a/video/end_to_end_tests/bandwidth_tests.cc b/video/end_to_end_tests/bandwidth_tests.cc
index 440a128..8c9ef05 100644
--- a/video/end_to_end_tests/bandwidth_tests.cc
+++ b/video/end_to_end_tests/bandwidth_tests.cc
@@ -140,12 +140,12 @@
 };
 
 TEST_F(BandwidthEndToEndTest, VerifySendSideBweStats) {
-  BandwidthStatsTest test(true, &task_queue_);
+  BandwidthStatsTest test(true, task_queue());
   RunBaseTest(&test);
 }
 
 TEST_F(BandwidthEndToEndTest, VerifyRecvSideBweStats) {
-  BandwidthStatsTest test(false, &task_queue_);
+  BandwidthStatsTest test(false, task_queue());
   RunBaseTest(&test);
 }
 
@@ -268,7 +268,7 @@
     TestState state_;
     RateLimiter retransmission_rate_limiter_;
     TaskQueueBase* const task_queue_;
-  } test(&task_queue_);
+  } test(task_queue());
 
   RunBaseTest(&test);
 }
@@ -364,7 +364,7 @@
     test::VideoEncoderProxyFactory encoder_factory_;
     std::unique_ptr<VideoBitrateAllocatorFactory> bitrate_allocator_factory_;
     uint32_t bitrate_kbps_ RTC_GUARDED_BY(crit_);
-  } test(&task_queue_);
+  } test(task_queue());
 
   RunBaseTest(&test);
 }