Use ScopedTaskEnvironment instead of MessageLoopForUI in components tests.

components/history/core/test/history_backend_db_base_test.cc

Index: components/history/core/test/history_backend_db_base_test.cc
diff --git a/components/history/core/test/history_backend_db_base_test.cc b/components/history/core/test/history_backend_db_base_test.cc
index 8a04b25c6a12161416ddcefb3e1c558812ec9768..f959858471e1a5575d112b17e3a67cf080704ff7 100644
--- a/components/history/core/test/history_backend_db_base_test.cc
+++ b/components/history/core/test/history_backend_db_base_test.cc
@@ -62,9 +62,10 @@ class BackendDelegate : public HistoryBackend::Delegate {
 };
 
 HistoryBackendDBBaseTest::HistoryBackendDBBaseTest()
-    : db_(nullptr),
-      last_profile_error_ (sql::INIT_OK) {
-}
+    : scoped_task_environment_(
+          base::test::ScopedTaskEnvironment::MainThreadType::UI),
+      db_(nullptr),
+      last_profile_error_(sql::INIT_OK) {}
 
 HistoryBackendDBBaseTest::~HistoryBackendDBBaseTest() {
 }