Introdcue AshWindowTreeHost and move ash/chrome specific code in WTH to ash.

ash/test/test_shell_delegate.cc

Index: ash/test/test_shell_delegate.cc
diff --git a/ash/test/test_shell_delegate.cc b/ash/test/test_shell_delegate.cc
index d2eeb108e159e243b4eefca462de40dfe80decd1..8ba5ba02562abb550b307a5db4f714994a6ed1f2 100644
--- a/ash/test/test_shell_delegate.cc
+++ b/ash/test/test_shell_delegate.cc
@@ -8,7 +8,6 @@
 
 #include "ash/default_accessibility_delegate.h"
 #include "ash/gpu_support_stub.h"
-#include "ash/host/window_tree_host_factory.h"
 #include "ash/media_delegate.h"
 #include "ash/new_window_delegate.h"
 #include "ash/session_state_delegate.h"
@@ -153,10 +152,6 @@ ui::MenuModel* TestShellDelegate::CreateContextMenu(
   return NULL;
 }
 
-WindowTreeHostFactory* TestShellDelegate::CreateWindowTreeHostFactory() {
-  return WindowTreeHostFactory::Create();
-}
-
 GPUSupport* TestShellDelegate::CreateGPUSupport() {
   // Real GPU support depends on src/content, so just use a stub.
   return new GPUSupportStub;