Revert "[NTP][RQ] Makes deletion of queries from in-memory URL DB asynchronous"

This reverts commit 49dbb543.

Reason for revert: Suspicious about making RepeatableQueriesServiceTest.SignedOut_Deletion flaky.
https://ci.chromium.org/p/chromium/builders/ci/Win7%20Tests%20%281%29?limit=200

Original change's description:
> [NTP][RQ] Makes deletion of queries from in-memory URL DB asynchronous
>
> Deletion from the in-memory URL DB can be slow: http://shortn/_eSkRG8RvpV
> This CL makes the deletion of queries from the in-memory URL DB async
> by posting the deletion task to a sequenced task runner on the UI thread.
>
> Fixed: 1110077
> Change-Id: Ia8099093eea6efde952bfbb58cd182b06174f8e7
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2531654
> Reviewed-by: Ramya Nagarajan <ramyan@chromium.org>
> Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#826399}

TBR=mahmadi@chromium.org,ramyan@chromium.org

Change-Id: I6377c865ef669849aa9f4fa484e80f3544531280
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532543Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826686}

components/search/repeatable_queries/repeatable_queries_service.cc

@@ -12,8 +12,6 @@
 #include "base/metrics/histogram_functions.h"
 #include "base/scoped_observer.h"
 #include "base/stl_util.h"
-#include "base/task/task_traits.h"
-#include "base/task/thread_pool.h"
 #include "base/values.h"
 #include "components/history/core/browser/history_service.h"
 #include "components/history/core/browser/history_types.h"
@@ -129,8 +127,7 @@ RepeatableQueriesService::RepeatableQueriesService(
       search_provider_observer_(std::make_unique<SearchProviderObserver>(
           template_url_service,
           base::BindRepeating(&RepeatableQueriesService::SearchProviderChanged,
-                              base::Unretained(this)))),
-      deletion_task_runner_(base::ThreadPool::CreateSequencedTaskRunner({})) {
+                              base::Unretained(this)))) {
   DCHECK(history_service_);
   DCHECK(template_url_service_);
   DCHECK(url_loader_factory_);
@@ -463,18 +460,8 @@ void RepeatableQueriesService::DeletionResponseLoaded(
 
 void RepeatableQueriesService::DeleteRepeatableQueryFromURLDatabase(
     const base::string16& query) {
-  deletion_task_runner_->PostTask(
-      FROM_HERE,
-      base::BindOnce(
-          &RepeatableQueriesService::DeleteRepeatableQueryFromURLDatabaseTask,
-          weak_ptr_factory_.GetWeakPtr(), query,
-          history_service_->InMemoryDatabase()));
-}
-
-void RepeatableQueriesService::DeleteRepeatableQueryFromURLDatabaseTask(
-    const base::string16& query,
-    history::URLDatabase* url_db) {
   // Fail if the in-memory URL database is not available.
+  history::URLDatabase* url_db = history_service_->InMemoryDatabase();
   if (!url_db)
     return;
 

components/search/repeatable_queries/repeatable_queries_service.h

@@ -19,13 +19,8 @@
 class SearchProviderObserver;
 class TemplateURLService;
 
-namespace base {
-class SequencedTaskRunner;
-}  // namespace base
-
 namespace history {
 class HistoryService;
-class URLDatabase;
 }  // namespace history
 
 namespace network {
@@ -140,8 +135,6 @@ class RepeatableQueriesService : public KeyedService {
 
   // Deletes |query| from the in-memory URLDatabase.
   void DeleteRepeatableQueryFromURLDatabase(const base::string16& query);
-  void DeleteRepeatableQueryFromURLDatabaseTask(const base::string16& query,
-                                                history::URLDatabase* url_db);
 
   // Deletes the query with |deletion_url| from the server.
   void DeleteRepeatableQueryFromServer(const std::string& deletion_url);
@@ -176,9 +169,6 @@ class RepeatableQueriesService : public KeyedService {
 
   std::vector<std::unique_ptr<network::SimpleURLLoader>> loaders_;
 
-  // The TaskRunner to which deletion tasks are posted.
-  scoped_refptr<base::SequencedTaskRunner> deletion_task_runner_;
-
   base::WeakPtrFactory<RepeatableQueriesService> weak_ptr_factory_{this};
 };