Migrate HidServiceLinux and HidConnectionLinux to BrowserThread::UI.

extensions/browser/api/hid/hid_apitest.cc

 // Copyright 2014 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/run_loop.h"
 #include "base/thread_task_runner_handle.h"
 #include "content/public/browser/browser_thread.h"
 #include "device/hid/hid_collection_info.h"
 #include "device/hid/hid_connection.h"
 #include "device/hid/hid_device_info.h"
@@ skipping 151 matching lines @@
                                             base::Bind(callback, connection));
   }
 };
 
 }  // namespace
 
 class HidApiTest : public ShellApiTest {
  public:
   void SetUpOnMainThread() override {
     ShellApiTest::SetUpOnMainThread();
+#if defined(OS_WIN)
+    // TODO(reillyg): Migrate Windows backend from FILE thread to UI thread.
     base::RunLoop run_loop;
-    BrowserThread::PostTaskAndReply(BrowserThread::FILE,
-                                    FROM_HERE,
+    BrowserThread::PostTaskAndReply(BrowserThread::FILE, FROM_HERE,
                                     base::Bind(&HidApiTest::SetUpService, this),
                                     run_loop.QuitClosure());
     run_loop.Run();
+#else
+    SetUpService();
+#endif
   }
 
   void SetUpService() { HidService::SetInstanceForTest(new MockHidService()); }
 };
 
 IN_PROC_BROWSER_TEST_F(HidApiTest, HidApp) {
   ASSERT_TRUE(RunAppTest("api_test/hid/api")) << message_;
 }
 
 }  // namespace extensions