Revert "Delete rtc::TaskQueue::Current in favor of webrtc::TaskQueueBase::Current"

This reverts commit 304e9d2df347630d71fd4423f5971f30dac73e41.

Reason for revert: Breaks downstream projects.
Seems to make VideoSendStreamTest.SupportsFlexfecSimulcastVp8 flaky.

Original change's description:
> Delete rtc::TaskQueue::Current in favor of webrtc::TaskQueueBase::Current
> 
> Bug: webrtc:10191
> Change-Id: I506cc50a90c73a6a4f6a3de36de0999cca72f5ba
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/126230
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#27035}

TBR=danilchap@webrtc.org,kwiberg@webrtc.org

Change-Id: If98324f88e4b3d18bf2fe33597dfb9711867c243
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:10191
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/126484
Reviewed-by: Yves Gerey <yvesg@webrtc.org>
Commit-Queue: Yves Gerey <yvesg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27041}
diff --git a/rtc_base/task_queue.h b/rtc_base/task_queue.h
index c42ce0f..1c0ae29 100644
--- a/rtc_base/task_queue.h
+++ b/rtc_base/task_queue.h
@@ -57,8 +57,8 @@
 //      private:
 //       bool Run() override {
 //         ++count_;
-//         TaskQueueBase::Current()->PostDelayedTask(
-//             absl::WrapUnique(this), 1000);
+//         TaskQueue::Current()->PostDelayedTask(
+//             std::unique_ptr<QueuedTask>(this), 1000);
 //         // Ownership has been transferred to the next occurance,
 //         // so return false to prevent from being deleted now.
 //         return false;
@@ -66,7 +66,8 @@
 //       int count_ = 0;
 //     };
 //     ...
-//     queue_.PostDelayedTask(absl::make_unique<TimerTask>(), 1000);
+//     queue_.PostDelayedTask(
+//         std::unique_ptr<QueuedTask>(new TimerTask()), 1000);
 //
 // For more examples, see task_queue_unittests.cc.
 //
@@ -89,6 +90,8 @@
                      Priority priority = Priority::NORMAL);
   ~TaskQueue();
 
+  static TaskQueue* Current();
+
   // Used for DCHECKing the current queue.
   bool IsCurrent() const;