Reactivate thread priority checks in ChromeOS tests

Thread priority should not be modified after a test.
If that is happening, it needs to be fixed in the code.

This CL remove the code that disable the priority checks.

NOTE TO SHERIFF:
 * please paste failure logs when reverting, the goal is
   to remove flaky tests related to thread priority.
 * assigned flaky test to etienneb@

Bug: 1097092
Change-Id: I086ceb10e88a657c91d8d4938e49ee85f7d66f7a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2295082Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#787791}

chrome/test/base/browser_tests_main_chromeos.cc

@@ -30,10 +30,8 @@ class BrowserTestSuiteRunnerChromeOS : public ChromeTestSuiteRunner {
  public:
   int RunTestSuite(int argc, char** argv) override {
     BrowserTestSuiteChromeOS test_suite(argc, argv);
-    // Browser tests are expected not to tear-down various globals and may
-    // complete with the thread priority being above NORMAL.
+    // Browser tests are expected not to tear-down various globals.
     test_suite.DisableCheckForLeakedGlobals();
-    test_suite.DisableCheckForThreadPriorityAtTestEnd();
     return test_suite.Run();
   }
 };