Use ScopedTaskEnvironment instead of MessageLoopForUI in ui tests.

ui/gfx/animation/slide_animation_unittest.cc

Index: ui/gfx/animation/slide_animation_unittest.cc
diff --git a/ui/gfx/animation/slide_animation_unittest.cc b/ui/gfx/animation/slide_animation_unittest.cc
index 9eb88d286034908cfb00239d4af5a81d8fac85fd..5de1700906ab43cb49401ad7d8ef04a495cd74a6 100644
--- a/ui/gfx/animation/slide_animation_unittest.cc
+++ b/ui/gfx/animation/slide_animation_unittest.cc
@@ -7,6 +7,7 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/time/time.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/animation/test_animation_delegate.h"
@@ -35,8 +36,13 @@ class SlideAnimation::TestApi {
 ////////////////////////////////////////////////////////////////////////////////
 // SlideAnimationTest
 class SlideAnimationTest: public testing::Test {
+ protected:
+  SlideAnimationTest()
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI) {}
+
  private:
-  base::MessageLoopForUI message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 // Tests animation construction.