Use ScopedTaskEnvironment instead of MessageLoop in...

Use ScopedTaskEnvironment instead of MessageLoop in /third_party/blink/renderer/platform/mojo/geometry_struct_traits_test.cc

MessageLoop will go away, eventually.

ScopedTaskEnvironment will per default start a ThreadPool, which should
be fine in most of the cases. If you belive your test needs to make sure
that no ThreadPool runs let me know and I will update the patch.

BUG=891670
This CL was uploaded by git cl split.

R=nasko@chromium.org

Change-Id: Id9b94f3da7bb55df8d0cfdeb399604cb85271e94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1649329
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Zhiqiang Zhang <zqzhang@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670073}

third_party/blink/renderer/platform/mojo/geometry_struct_traits_test.cc

@@ -4,7 +4,7 @@
 
 #include <utility>
 
-#include "base/message_loop/message_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/geometry/mojo/geometry.mojom-blink.h"
@@ -93,7 +93,7 @@ class GeometryStructTraitsTest
   mojo::BindingSet<gfx::mojom::blink::GeometryTraitsTestService>
       traits_test_bindings_;
 
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 
   DISALLOW_COPY_AND_ASSIGN(GeometryStructTraitsTest);
 };