Revert "history service: Turn DCHECKs to CHECKs to try to diagnose crash bug."

This reverts commit ee5f0d37.

Reason for revert: This CL has no effect because the |thread_checker_| in the class is a no-op implementation in Release builds. Will re-land a version of this CL that fixes that, in a single CL, so it's easy to revert.

Original change's description:
> history service: Turn DCHECKs to CHECKs to try to diagnose crash bug.
> 
> Bug: 1009795
> Change-Id: Ib33c1242228e674442f21dea8a56ef456d84b886
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1899231
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: Matt Falkenhagen <falken@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#712948}

TBR=falken@chromium.org,sky@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1009795
Change-Id: I24a8c7ff548d43c315528e85556967800336aea9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918120Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715466}

components/history/core/browser/history_service.cc

@@ -491,10 +491,8 @@ base::CancelableTaskTracker::TaskId HistoryService::GetFaviconsForURL(
     favicon_base::FaviconResultsCallback callback,
     base::CancelableTaskTracker* tracker) {
   TRACE_EVENT0("browser", "HistoryService::GetFaviconsForURL");
-  // TODO(crbug.com/1009795): Return the CHECKs to DCHECKs after the bug is
-  // fixed.
-  CHECK(thread_checker_.CalledOnValidThread());
-  CHECK(backend_task_runner_) << "History service being called after cleanup";
+  DCHECK(backend_task_runner_) << "History service being called after cleanup";
+  DCHECK(thread_checker_.CalledOnValidThread());
   return tracker->PostTaskAndReplyWithResult(
       backend_task_runner_.get(), FROM_HERE,
       base::BindOnce(&HistoryBackend::GetFaviconsForURL, history_backend_,
@@ -642,10 +640,8 @@ void HistoryService::SetOnDemandFavicons(
     const GURL& icon_url,
     const std::vector<SkBitmap>& bitmaps,
     base::OnceCallback<void(bool)> callback) {
-  // TODO(crbug.com/1009795): Return the CHECKs to DCHECKs after the bug is
-  // fixed.
-  CHECK(thread_checker_.CalledOnValidThread());
-  CHECK(backend_task_runner_) << "History service being called after cleanup";
+  DCHECK(backend_task_runner_) << "History service being called after cleanup";
+  DCHECK(thread_checker_.CalledOnValidThread());
   if (history_client_ && !history_client_->CanAddURL(page_url)) {
     std::move(callback).Run(false);
     return;