Disable `SitePerProcessBrowserTest.OOPIFDetachDuringAnimation` on ChromeOS.

[1] shows that `SitePerProcessBrowserTest.OOPIFDetachDuringAnimation` is
somewhat flaky in general, and it just flaked twice in a row this morning on
`linux-chromeos-rel`: [2], [3]

[1]: https://analysis.chromium.org/p/chromium/flake-portal/flakes/occurrences?key=ag9zfmZpbmRpdC1mb3ItbWVyXQsSBUZsYWtlIlJjaHJvbWl1bUBjb250ZW50X2Jyb3dzZXJ0ZXN0c0BTaXRlUGVyUHJvY2Vzc0Jyb3dzZXJUZXN0Lk9PUElGRGV0YWNoRHVyaW5nQW5pbWF0aW9uDA&show_all_occurrences=1
[2]: https://ci.chromium.org/p/chromium/builders/ci/linux-chromeos-rel/31228
[3]: https://ci.chromium.org/p/chromium/builders/ci/linux-chromeos-rel/31229

TBR=kenrb@chromium.org

Bug: 809580
Change-Id: I866bfc20a69e706aee34addd32a5e8e8fc40792f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1912710Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714883}

content/browser/site_per_process_browsertest.cc

@@ -11821,9 +11821,9 @@ class CommitMessageOrderReverser : public DidCommitNavigationInterceptor {
 
 // Create an out-of-process iframe that causes itself to be detached during
 // its layout/animate phase. See https://crbug.com/802932.
-// Disabled on Android due to flakiness, https://crbug.com/809580.
-// Disabled on Mac due to flakiness, https://crbug.com/1006122.
-#if defined(OS_ANDROID) || defined(OS_MACOSX)
+//
+// TODO(809580): Disabled on Android, Mac, and ChromeOS due to flakiness.
+#if defined(OS_ANDROID) || defined(OS_MACOSX) || defined(OS_CHROMEOS)
 #define MAYBE_OOPIFDetachDuringAnimation DISABLED_OOPIFDetachDuringAnimation
 #else
 #define MAYBE_OOPIFDetachDuringAnimation OOPIFDetachDuringAnimation