Use ScopedTaskEnvironment instead of MessageLoopForUI in ui tests.

ui/gfx/animation/animation_container_unittest.cc

Index: ui/gfx/animation/animation_container_unittest.cc
diff --git a/ui/gfx/animation/animation_container_unittest.cc b/ui/gfx/animation/animation_container_unittest.cc
index ae29d8ad2cfba080f1cd52d33cb23b6ac86ee7d7..003ae32d70af177f5c669360c01c0f8b19ad7d01 100644
--- a/ui/gfx/animation/animation_container_unittest.cc
+++ b/ui/gfx/animation/animation_container_unittest.cc
@@ -8,6 +8,7 @@
 
 #include "base/macros.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/animation/animation_container_observer.h"
 #include "ui/gfx/animation/linear_animation.h"
@@ -58,8 +59,13 @@ class TestAnimation : public LinearAnimation {
 }  // namespace
 
 class AnimationContainerTest: public testing::Test {
+ protected:
+  AnimationContainerTest()
+      : scoped_task_environment_(
+            base::test::ScopedTaskEnvironment::MainThreadType::UI) {}
+
  private:
-  base::MessageLoopForUI message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 // Makes sure the animation ups the ref count of the container and releases it