Prepare HistoryService tests for HistoryServiceUsesTaskScheduler activation.

The feature will soon be flipped to ENABLED_BY_DEFAULT. This will make
HistoryServiceBackend's task runner dispatch to the ThreadPool instead
of a dedicated base::Thread. The tests need to be prepared to stay
functional when that happens.

This is done as the last mile of the chrome-wide effort to coalesce as
much work as possible to the ThreadPool.

Bug: 661143
Change-Id: I7bdbdb5152edafc5394aeab187ea8a8602f5330e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1972305
Commit-Queue: Oliver Li <olivierli@chromium.org>
Auto-Submit: Oliver Li <olivierli@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726361}

components/history/core/browser/history_backend_unittest.cc

@@ -241,6 +241,7 @@ class HistoryBackendTestBase : public testing::Test {
     mem_backend_->OnKeywordSearchTermDeleted(nullptr, url_id);
   }
 
+  base::test::TaskEnvironment task_environment_;
   history::HistoryClientFakeBookmarks history_client_;
   scoped_refptr<HistoryBackend> backend_;  // Will be NULL on init failure.
   std::unique_ptr<InMemoryHistoryBackend> mem_backend_;
@@ -282,7 +283,6 @@ class HistoryBackendTestBase : public testing::Test {
   URLsModifiedList urls_modified_notifications_;
   URLsDeletedList urls_deleted_notifications_;
 
-  base::test::SingleThreadTaskEnvironment task_environment_;
   base::FilePath test_dir_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackendTestBase);
@@ -3578,28 +3578,6 @@ TEST_F(HistoryBackendTest, DeleteMatchingUrlsForKeyword) {
   EXPECT_FALSE(backend_->db()->GetKeywordSearchTermRow(url3_id, nullptr));
 }
 
-// Simple test that removes a bookmark. This test exercises the code paths in
-// History that block till bookmark bar model is loaded.
-TEST_F(HistoryBackendTest, RemoveNotification) {
-  base::ScopedTempDir scoped_temp_dir;
-  EXPECT_TRUE(scoped_temp_dir.CreateUniqueTempDirUnderPath(test_dir()));
-
-  // Add a URL.
-  GURL url("http://www.google.com");
-  std::unique_ptr<HistoryService> service(
-      new HistoryService(std::make_unique<HistoryClientFakeBookmarks>(),
-                         std::unique_ptr<history::VisitDelegate>()));
-  EXPECT_TRUE(service->Init(
-      TestHistoryDatabaseParamsForPath(scoped_temp_dir.GetPath())));
-
-  service->AddPage(url, base::Time::Now(), nullptr, 1, GURL(), RedirectList(),
-                   ui::PAGE_TRANSITION_TYPED, SOURCE_BROWSED, false);
-
-  // This won't actually delete the URL, rather it'll empty out the visits.
-  // This triggers blocking on the BookmarkModel.
-  service->DeleteURLs({url});
-}
-
 // Test DeleteFTSIndexDatabases deletes expected files.
 TEST_F(HistoryBackendTest, DeleteFTSIndexDatabases) {
   ASSERT_TRUE(backend_.get());

components/history/core/browser/history_querying_unittest.cc

@@ -194,7 +194,7 @@ class HistoryQueryTest : public testing::Test {
 
   base::ScopedTempDir temp_dir_;
 
-  base::test::SingleThreadTaskEnvironment task_environment_;
+  base::test::TaskEnvironment task_environment_;
 
   base::FilePath history_dir_;
 

components/history/core/browser/history_service_unittest.cc

@@ -58,10 +58,7 @@ namespace history {
 
 class HistoryServiceTest : public testing::Test {
  public:
-  HistoryServiceTest()
-      : task_environment_(
-            base::test::SingleThreadTaskEnvironment::MainThreadType::UI) {}
-
+  HistoryServiceTest() = default;
   ~HistoryServiceTest() override {}
 
  protected:
@@ -156,7 +153,7 @@ class HistoryServiceTest : public testing::Test {
 
   base::ScopedTempDir temp_dir_;
 
-  base::test::SingleThreadTaskEnvironment task_environment_;
+  base::test::TaskEnvironment task_environment_;
 
   MostVisitedURLList most_visited_urls_;
 
@@ -179,6 +176,23 @@ class HistoryServiceTest : public testing::Test {
   history::QueryURLResult query_url_result_;
 };
 
+// Simple test that removes a bookmark. This test exercises the code paths in
+// History that block till BookmarkModel is loaded.
+TEST_F(HistoryServiceTest, RemoveNotification) {
+  ASSERT_TRUE(history_service_.get());
+
+  // Add a URL.
+  GURL url("http://www.google.com");
+
+  history_service_->AddPage(url, base::Time::Now(), nullptr, 1, GURL(),
+                            RedirectList(), ui::PAGE_TRANSITION_TYPED,
+                            SOURCE_BROWSED, false);
+
+  // This won't actually delete the URL, rather it'll empty out the visits.
+  // This triggers blocking on the BookmarkModel.
+  history_service_->DeleteURLs({url});
+}
+
 TEST_F(HistoryServiceTest, AddPage) {
   ASSERT_TRUE(history_service_.get());
   // Add the page once from a child frame.