TestMockTimeTaskRunner: Remove just added CHECKs on posts to dead one

Turns out these are just too hard to avoid when TestMockTimeTaskRunner
is used in a browser test.

Bug: 860092
Change-Id: I11e3dcfacf073549c56a40eb6840de1df4a52896
Reviewed-on: https://chromium-review.googlesource.com/1127930
Commit-Queue: Maks Orlovich <morlovich@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573565}

base/test/test_mock_time_task_runner.cc

@@ -87,24 +87,29 @@ class TestMockTimeTaskRunner::NonOwningProxyTaskRunner
       return target_->RunsTasksInCurrentSequence();
     return thread_checker_.CalledOnValidThread();
   }
+
   bool PostDelayedTask(const Location& from_here,
                        OnceClosure task,
                        TimeDelta delay) override {
     AutoLock scoped_lock(lock_);
-    CHECK(target_)
-        << "Attempt to post a task on a deleted TestMockTimeTaskRunner";
+    if (target_)
+      return target_->PostDelayedTask(from_here, std::move(task), delay);
 
-    return target_->PostDelayedTask(from_here, std::move(task), delay);
+    // The associated TestMockTimeTaskRunner is dead, so fail this PostTask.
+    return false;
   }
+
   bool PostNonNestableDelayedTask(const Location& from_here,
                                   OnceClosure task,
                                   TimeDelta delay) override {
     AutoLock scoped_lock(lock_);
-    CHECK(target_)
-        << "Attempt to post a task on a deleted TestMockTimeTaskRunner";
+    if (target_) {
+      return target_->PostNonNestableDelayedTask(from_here, std::move(task),
+                                                 delay);
+    }
 
-    return target_->PostNonNestableDelayedTask(from_here, std::move(task),
-                                               delay);
+    // The associated TestMockTimeTaskRunner is dead, so fail this PostTask.
+    return false;
   }
 
  private:

chrome/browser/chromeos/login/wizard_controller_browsertest.cc

@@ -1626,9 +1626,8 @@ IN_PROC_BROWSER_TEST_F(WizardControllerDeviceStateWithInitialEnrollmentTest,
       5 /* NotRequiredInEmbargoPeriod*/, 1 /* count */);
 }
 
-// Disabled because it's flaky: crbug.com/860092.
 IN_PROC_BROWSER_TEST_F(WizardControllerDeviceStateWithInitialEnrollmentTest,
-                       DISABLED_ControlFlowWaitSystemClockSyncTimeout) {
+                       ControlFlowWaitSystemClockSyncTimeout) {
   auto task_runner = base::MakeRefCounted<base::TestMockTimeTaskRunner>();
 
   base::TestMockTimeTaskRunner::ScopedContext scoped_context(task_runner);