overview: Remove a debugging log.

TBR=manucornet@chromium.org

Test: none
Bug: none
Change-Id: Ibe2345c3eea249271da956d3f23ad89785ba7210
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881316Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709587}

ash/wm/overview/overview_controller.cc

@@ -464,7 +464,6 @@ void OverviewController::ToggleOverview(
   } else {
     DCHECK(CanEnterOverview());
     TRACE_EVENT_ASYNC_BEGIN0("ui", "OverviewController::EnterOverview", this);
-    LOG(ERROR) << "Will start, overview session " << overview_session();
     for (auto& observer : observers_)
       observer.OnOverviewModeWillStart();