3rd part of porting Chrome Ash to Windows 7

ash/host/ash_window_tree_host_win.cc

Index: ash/host/ash_window_tree_host_win.cc
diff --git a/ash/host/ash_window_tree_host_win.cc b/ash/host/ash_window_tree_host_win.cc
index 5ea0f4a1ae5e5b0ab062c9f2a8217d9899952996..27fd5a47f9e8e49b8d06f007ea113c85a8fe817d 100644
--- a/ash/host/ash_window_tree_host_win.cc
+++ b/ash/host/ash_window_tree_host_win.cc
@@ -108,7 +108,7 @@ class ASH_EXPORT AshWindowTreeHostWin : public AshWindowTreeHost,
 }  // namespace
 
 AshWindowTreeHost* AshWindowTreeHost::Create(const gfx::Rect& initial_bounds) {
-  if (base::win::GetVersion() >= base::win::VERSION_WIN8 &&
+  if (base::win::GetVersion() >= base::win::VERSION_WIN7 &&
       !CommandLine::ForCurrentProcess()->HasSwitch(
           ash::switches::kForceAshToDesktop))
     return AshRemoteWindowTreeHostWin::GetInstance();