X11: Add TestDesktopScreenX11 to simulate mouse movement in ui tests

chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc

Index: chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
diff --git a/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc b/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
index 7cf64a2a989d34ce043c83fb3efd4ab15f5930b5..e3de8fe5c6b2e6ad834e71a0a2a8ec690f654852 100644
--- a/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
+++ b/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
@@ -45,7 +45,9 @@ void ChromeBrowserMainExtraPartsViews::ToolkitInitialized() {
 
 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
 }