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

ash/test/test_suite.cc

Index: ash/test/test_suite.cc
diff --git a/ash/test/test_suite.cc b/ash/test/test_suite.cc
index f606829fc2d3de13904f55a2db5658ca61d8c870..a42a6859a76ced6a0185dce96415e46d07d4c877 100644
--- a/ash/test/test_suite.cc
+++ b/ash/test/test_suite.cc
@@ -4,6 +4,8 @@
 
 #include "ash/test/test_suite.h"
 
+#include "ash/ash_switches.h"
+#include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/path_service.h"
 #include "build/build_config.h"
@@ -36,7 +38,9 @@ void AuraShellTestSuite::Initialize() {
   base::TestSuite::Initialize();
 
 #if defined(OS_WIN)
-  if (base::win::GetVersion() >= base::win::VERSION_WIN8) {
+  if (base::win::GetVersion() >= base::win::VERSION_WIN8 &&
+      !CommandLine::ForCurrentProcess()->HasSwitch(
+          ash::switches::kForceAshToDesktop)) {
     ASSERT_TRUE(win8::RegisterTestDefaultBrowser(
         win8::test::kDefaultTestAppUserModelId,
         win8::test::kDefaultTestExeName));