Remove one ExecutionTask constructor

There is no usage of the constructor.

Change-Id: I23cfe086745d2d6b395ee4a6e29c64304504a1d4
Reviewed-on: https://chromium-review.googlesource.com/1118075Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571093}

third_party/blink/renderer/platform/scheduler/base/task_queue_manager_impl.h

@@ -177,11 +177,6 @@ class PLATFORM_EXPORT TaskQueueManagerImpl
   // selector interface is unaware of those.  This struct keeps track off all
   // task related state needed to make pairs of TakeTask() / DidRunTask() work.
   struct ExecutingTask {
-    ExecutingTask()
-        : pending_task(TaskQueue::PostedTask(OnceClosure(), Location()),
-                       TimeTicks(),
-                       internal::EnqueueOrder()) {}
-
     ExecutingTask(internal::TaskQueueImpl::Task&& pending_task,
                   internal::TaskQueueImpl* task_queue)
         : pending_task(std::move(pending_task)), task_queue(task_queue) {}