[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/+/2531654Reviewed-by: Ramya Nagarajan <ramyan@chromium.org>
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826399}

components/search/repeatable_queries/repeatable_queries_service.cc

@@ -12,6 +12,8 @@
 #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"
@@ -127,7 +129,8 @@ RepeatableQueriesService::RepeatableQueriesService(
       search_provider_observer_(std::make_unique<SearchProviderObserver>(
           template_url_service,
           base::BindRepeating(&RepeatableQueriesService::SearchProviderChanged,
-                              base::Unretained(this)))) {
+                              base::Unretained(this)))),
+      deletion_task_runner_(base::ThreadPool::CreateSequencedTaskRunner({})) {
   DCHECK(history_service_);
   DCHECK(template_url_service_);
   DCHECK(url_loader_factory_);
@@ -460,8 +463,18 @@ 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

@@ -19,8 +19,13 @@
 class SearchProviderObserver;
 class TemplateURLService;
 
+namespace base {
+class SequencedTaskRunner;
+}  // namespace base
+
 namespace history {
 class HistoryService;
+class URLDatabase;
 }  // namespace history
 
 namespace network {
@@ -135,6 +140,8 @@ 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);
@@ -169,6 +176,9 @@ 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};
 };