Disable flaky test PreviousTrackButtonVisibility on Linux

Bug: 985303
Change-Id: I53790b1d5f2dc7375b5b9362ea7b07db981d664f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2556860
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Auto-Submit: Wojciech Dzierżanowski <wdzierzanowski@opera.com>
Reviewed-by: François Beaufort <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/master@{#830535}

chrome/browser/picture_in_picture/picture_in_picture_window_controller_browsertest.cc

@@ -2093,8 +2093,15 @@ IN_PROC_BROWSER_TEST_F(MediaSessionPictureInPictureWindowControllerBrowserTest,
 
 // Tests that a Previous Track button is displayed in the Picture-in-Picture
 // window when Media Session Action "previoustrack" is handled by the website.
+// TODO(crbug.com/985303): Flaky on Linux.
+#if defined(OS_LINUX)
+#define MAYBE_PreviousTrackButtonVisibility \
+  DISABLED_PreviousTrackButtonVisibility
+#else
+#define MAYBE_PreviousTrackButtonVisibility PreviousTrackButtonVisibility
+#endif
 IN_PROC_BROWSER_TEST_F(MediaSessionPictureInPictureWindowControllerBrowserTest,
-                       PreviousTrackButtonVisibility) {
+                       MAYBE_PreviousTrackButtonVisibility) {
   LoadTabAndEnterPictureInPicture(
       browser(), base::FilePath(kPictureInPictureWindowSizePage));
   OverlayWindowViews* overlay_window = static_cast<OverlayWindowViews*>(