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

chrome/browser/ui/aura/chrome_browser_main_extra_parts_aura.cc

Index: chrome/browser/ui/aura/chrome_browser_main_extra_parts_aura.cc
diff --git a/chrome/browser/ui/aura/chrome_browser_main_extra_parts_aura.cc b/chrome/browser/ui/aura/chrome_browser_main_extra_parts_aura.cc
index b878bd148162bcb54b05fb4956155a1bb3e22bfd..db04a542768f2a87dc30fee98e45f0c67dd87514 100644
--- a/chrome/browser/ui/aura/chrome_browser_main_extra_parts_aura.cc
+++ b/chrome/browser/ui/aura/chrome_browser_main_extra_parts_aura.cc
@@ -16,6 +16,7 @@
 #include "ui/aura/env.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/ui_base_switches.h"
+#include "ui/gfx/dpi.h"
 #include "ui/gfx/screen.h"
 #include "ui/views/widget/native_widget_aura.h"
 
@@ -93,6 +94,7 @@ void ChromeBrowserMainExtraPartsAura::PreEarlyInitialization() {
     views::LinuxUI* gtk2_ui = BuildGtk2UI();
     gtk2_ui->SetNativeThemeOverride(base::Bind(&GetNativeThemeForWindow));
     views::LinuxUI::SetInstance(gtk2_ui);
+    gfx::InitDeviceScaleFactor(gfx::GetDPIScale());
   } else {
     // TODO(erg): Eventually, we'll need to somehow support IMEs in ash on
     // Linux.