Move gtk-specific browser main parts stuff to its own file.

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 f10252d7fae61e5655acd4fd973c24c6054a359b..3206b65064c043d122031068354cd519a0158ce9 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
@@ -9,6 +9,8 @@
 #include "components/constrained_window/constrained_window_views.h"
 
 #if defined(USE_AURA)
+#include "ui/gfx/screen.h"
+#include "ui/views/widget/desktop_aura/desktop_screen.h"
 #include "ui/wm/core/wm_state.h"
 #endif
 
@@ -31,3 +33,9 @@ void ChromeBrowserMainExtraPartsViews::ToolkitInitialized() {
   wm_state_.reset(new wm::WMState);
 #endif
 }
+
+void ChromeBrowserMainExtraPartsViews::PreCreateThreads() {
+#if defined(USE_AURA) && !defined(OS_CHROMEOS)
+  gfx::Screen::SetScreenInstance(views::CreateDesktopScreen());
+#endif
+}