Revert "Mark DialogClientViewTest.ButtonPosition flaky on Mac"

This reverts commit 77e3d644.

Reason for revert: he test flakiness is caused by bot flakiness.

Original change's description:
> Mark DialogClientViewTest.ButtonPosition flaky on Mac
> 
> This patch marks DialogClientViewTest.ButtonPosition flaky on Mac.
> 
> TBR=bsep@chromium.org
> 
> Bug: 903000
> Change-Id: I7d533956e437c143e4d4030dd357553fd4caabf1
> Reviewed-on: https://chromium-review.googlesource.com/c/1325592
> Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
> Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#606338}

TBR=yosin@chromium.org

Change-Id: Ib253d9870dcbae3ca12ccba6b7db76d0c34afd7e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 903000
Reviewed-on: https://chromium-review.googlesource.com/c/1325279Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606345}

ui/views/window/dialog_client_view_unittest.cc

@@ -453,13 +453,7 @@ TEST_F(DialogClientViewTest, LinkedWidths) {
   EXPECT_EQ(20, boring_view->width());
 }
 
-// TODO(crbug.com/903000): We should not mark GetIndexOf flaky.
-#if defined(OS_MACOSX)
-#define MAYBE_ButtonPosition DISABLED_ButtonPosition
-#else
-#define MAYBE_ButtonPosition ButtonPosition
-#endif
-TEST_F(DialogClientViewTest, MAYBE_ButtonPosition) {
+TEST_F(DialogClientViewTest, ButtonPosition) {
   constexpr int button_row_inset = 13;
   client_view()->SetButtonRowInsets(gfx::Insets(button_row_inset));
   constexpr int contents_height = 37;