Enable hidpi on Linux, refactor a bit on Windows to share

ash/test/test_metro_viewer_process_host.cc

 // Copyright (c) 2013 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 "ash/test/test_metro_viewer_process_host.h"
 
 #include <windef.h>
 
 #include "base/logging.h"
 #include "ui/aura/remote_window_tree_host_win.h"
-#include "ui/gfx/win/dpi.h"
+#include "ui/gfx/dpi.h"
 
 namespace ash {
 namespace test {
 
 TestMetroViewerProcessHost::TestMetroViewerProcessHost(
     base::SingleThreadTaskRunner* ipc_task_runner)
     : MetroViewerProcessHost(ipc_task_runner),
       closed_unexpectedly_(false) {
 }
 
@@ skipping 37 matching lines @@
 void TestMetroViewerProcessHost::OnHandleSearchRequest(
     const base::string16& search_string) {
 }
 
 void TestMetroViewerProcessHost::OnWindowSizeChanged(uint32 width,
                                                      uint32 height) {
 }
 
 }  // namespace test
 }  // namespace ash