X11: Add TestDesktopScreenX11 to simulate mouse movement in ui tests

chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc

 // Copyright (c) 2012 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 "chrome/browser/ui/views/chrome_browser_main_extra_parts_views.h"
 
 #include "chrome/browser/ui/views/chrome_constrained_window_views_client.h"
 #include "chrome/browser/ui/views/chrome_views_delegate.h"
 #include "components/constrained_window/constrained_window_views.h"
 
@@ skipping 27 matching lines @@
 
   SetConstrainedWindowViewsClient(CreateChromeConstrainedWindowViewsClient());
 
 #if defined(USE_AURA)
   wm_state_.reset(new wm::WMState);
 #endif
 }
 
 void ChromeBrowserMainExtraPartsViews::PreCreateThreads() {
 #if defined(USE_AURA) && !defined(OS_CHROMEOS)
-  display::Screen::SetScreenInstance(views::CreateDesktopScreen());
+  // The screen may have already been set in test initialization.
+  if (!display::Screen::GetScreen())
+    display::Screen::SetScreenInstance(views::CreateDesktopScreen());
 #endif
 }
 
 void ChromeBrowserMainExtraPartsViews::MojoShellConnectionStarted(
     content::MojoShellConnection* connection) {
   DCHECK(connection);
 #if defined(USE_AURA)
   if (shell::ShellIsRemote()) {
     // TODO(rockot): Remove the blocking wait for init.
     // http://crbug.com/594852.
     base::RunLoop wait_loop;
     connection->SetInitializeHandler(wait_loop.QuitClosure());
     wait_loop.Run();
 
     input_device_client_.reset(new ui::InputDeviceClient());
     ui::mojom::InputDeviceServerPtr server;
     connection->GetConnector()->ConnectToInterface("mojo:ui", &server);
     input_device_client_->Connect(std::move(server));
 
     window_manager_connection_ = views::WindowManagerConnection::Create(
         connection->GetConnector(), connection->GetIdentity(),
         content::BrowserThread::GetTaskRunnerForThread(
             content::BrowserThread::IO));
   }
 #endif  // defined(USE_AURA)
 }