Add switch to run ash tests on desktop in windows 8.

ash/host/root_window_host_factory_win.cc

Index: ash/host/root_window_host_factory_win.cc
diff --git a/ash/host/root_window_host_factory_win.cc b/ash/host/root_window_host_factory_win.cc
index 1703b727dbaf308d3339e4aabc90fc9e31906cc5..5dceef90be0c0334bdfdeb2dab507fbc65390d4e 100644
--- a/ash/host/root_window_host_factory_win.cc
+++ b/ash/host/root_window_host_factory_win.cc
@@ -4,6 +4,8 @@
 
 #include "ash/host/root_window_host_factory.h"
 
+#include "ash/ash_switches.h"
+#include "base/command_line.h"
 #include "base/win/windows_version.h"
 #include "ui/aura/remote_root_window_host_win.h"
 #include "ui/aura/root_window_host.h"
@@ -17,7 +19,9 @@ class RootWindowHostFactoryImpl : public ash::RootWindowHostFactory {
   // Overridden from RootWindowHostFactory:
   virtual aura::RootWindowHost* CreateRootWindowHost(
       const gfx::Rect& initial_bounds) OVERRIDE {
-    if (base::win::GetVersion() >= base::win::VERSION_WIN8)
+    if (base::win::GetVersion() >= base::win::VERSION_WIN8 &&
+        !CommandLine::ForCurrentProcess()->HasSwitch(
+            ash::switches::kForceAshToDesktop))
       return aura::RemoteRootWindowHostWin::Create(initial_bounds);
 
     return aura::RootWindowHost::Create(initial_bounds);