Use ScopedTaskEnvironment instead of MessageLoop in components unit tests.

components/suggestions/image_manager_unittest.cc

Index: components/suggestions/image_manager_unittest.cc
diff --git a/components/suggestions/image_manager_unittest.cc b/components/suggestions/image_manager_unittest.cc
index e9c139eb9a0a220caab58489d9024aaf4341ea52..0966a21a7f135fb9b81313a4f6c9d6f44e1261f4 100644
--- a/components/suggestions/image_manager_unittest.cc
+++ b/components/suggestions/image_manager_unittest.cc
@@ -10,6 +10,7 @@
 #include "base/files/file_path.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/image_fetcher/core/image_fetcher.h"
 #include "components/image_fetcher/core/image_fetcher_delegate.h"
@@ -139,7 +140,7 @@ class ImageManagerTest : public testing::Test {
   int num_callback_null_called_;
   int num_callback_valid_called_;
 
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 
   // Under test.
   std::unique_ptr<ImageManager> image_manager_;