Revert "Mark ViewTest.GetIndexOf flaky on Mac"

This reverts commit 1724744c.

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

Original change's description:
> Mark ViewTest.GetIndexOf flaky on Mac
> 
> This patch marks ViewTest.GetIndexOf flaky on Mac.
> 
> TBR=tfarina@chromium.org, sky@chromium.org
> 
> Bug: 903002
> Change-Id: Ic8a82a9f09de1dab8a201c23452b86a3714f54be
> Reviewed-on: https://chromium-review.googlesource.com/c/1325571
> Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
> Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#606330}

TBR=yosin@chromium.org

Change-Id: I2d0fffa6740ab614081632ea6a0bc08e26c6069f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 903002
Reviewed-on: https://chromium-review.googlesource.com/c/1325593Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606343}

ui/views/view_unittest.cc

@@ -3537,13 +3537,7 @@ TEST_F(ViewTest, Contains) {
 // +-- child1
 //     +-- foo1
 // +-- child2
-// TODO(crbug.com/903002): We should not mark GetIndexOf flaky.
-#if defined(OS_MACOSX)
-#define MAYBE_GetIndexOf DISABLED_GetIndexOf
-#else
-#define MAYBE_GetIndexOf GetIndexOf
-#endif
-TEST_F(ViewTest, MAYBE_GetIndexOf) {
+TEST_F(ViewTest, GetIndexOf) {
   View root;
 
   View* child1 = new View;