TaskScheduler: No BACKGROUND threads when unsupported.

base/task_scheduler/task_scheduler_impl_unittest.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/task_scheduler/task_scheduler_impl.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/synchronization/lock.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/task_scheduler/scheduler_worker_pool_params.h"
 #include "base/task_scheduler/task_traits.h"
 #include "base/task_scheduler/test_task_factory.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/simple_thread.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/time/time.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 18 matching lines @@
   const bool previous_value = ThreadRestrictions::SetIOAllowed(true);
   ThreadRestrictions::SetIOAllowed(previous_value);
   return previous_value;
 }
 #endif
 
 // Verify that the current thread priority and I/O restrictions are appropriate
 // to run a Task with |traits|.
 // Note: ExecutionMode is verified inside TestTaskFactory.
 void VerifyTaskEnvironement(const TaskTraits& traits) {
-  EXPECT_EQ(traits.priority() == TaskPriority::BACKGROUND
+  const bool supports_background_priority =
+      Lock::HandlesMultipleThreadPriorities() &&
+      PlatformThread::CanIncreaseCurrentThreadPriority();
+
+  EXPECT_EQ(supports_background_priority &&
+                    traits.priority() == TaskPriority::BACKGROUND
                 ? ThreadPriority::BACKGROUND
                 : ThreadPriority::NORMAL,
             PlatformThread::GetCurrentThreadPriority());
 
 #if DCHECK_IS_ON()
   // The #if above is required because GetIOAllowed() always returns true when
   // !DCHECK_IS_ON(), even when |traits| don't allow file I/O.
   EXPECT_EQ(traits.with_file_io(), GetIOAllowed());
 #endif
 
@@ skipping 185 matching lines @@
     thread->WaitForAllTasksToRun();
     thread->Join();
   }
 }
 
 // TODO(fdoray): Add tests with Sequences that move around worker pools once
 // child TaskRunners are supported.
 
 }  // namespace internal
 }  // namespace base