Backport some tests in /components/browsing_data to SingleThreadTaskEnvironment

These tests were previously migrated from single-threaded MessageLoop to
a multi-threaded TaskEnvironment (then named ScopedTaskEnvironment) as
part of crbug.com/891670.

//base OWNERS decided in retrospect that it was better to keep a
single-threaded option for TaskEnvironment and introduced
SingleThreadTaskEnvironment. This CL retrofits that decision for
/components/browsing_data.

This CL is a no-op if it passes CQ.

This CL was uploaded by git cl split.

R=dullweber@chromium.org

Bug: 891670
Change-Id: I31e0a16f1dc0e605fad78e6252ec7d7a833efb9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1786839
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694883}

components/browsing_data/core/browsing_data_utils_unittest.cc

@@ -50,7 +50,7 @@ class BrowsingDataUtilsTest : public testing::Test {
   PrefService* prefs() { return &prefs_; }
 
  private:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   sync_preferences::TestingPrefServiceSyncable prefs_;
 };
 

components/browsing_data/core/counters/browsing_data_counter_unittest.cc

@@ -104,7 +104,7 @@ class BrowsingDataCounterTest : public testing::Test {
  private:
   std::unique_ptr<TestingPrefServiceSimple> pref_service_;
   std::unique_ptr<MockBrowsingDataCounter> counter_;
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
 };
 
 TEST_F(BrowsingDataCounterTest, NoResponse) {