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

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 4c12d322a5359dd7e30e1f257cfeeea142a2d0c2..bdbbd1853b2faa97e164fb620ff3faefe103324a 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -29,7 +29,6 @@
 #include "ash/frame/custom_frame_view_ash.h"
 #include "ash/gpu_support.h"
 #include "ash/high_contrast/high_contrast_controller.h"
-#include "ash/host/window_tree_host_factory.h"
 #include "ash/keyboard_uma_event_filter.h"
 #include "ash/magnifier/magnification_controller.h"
 #include "ash/magnifier/partial_magnification_controller.h"
@@ -843,10 +842,9 @@ void Shell::Init() {
   focus_cycler_.reset(new internal::FocusCycler());
 
   screen_position_controller_.reset(new internal::ScreenPositionController);
-  window_tree_host_factory_.reset(delegate_->CreateWindowTreeHostFactory());
 
   display_controller_->Start();
-  display_controller_->InitPrimaryDisplay();
+  display_controller_->CreatePrimaryHost();
   aura::Window* root_window = display_controller_->GetPrimaryRootWindow();
   target_root_window_ = root_window;
 
@@ -983,13 +981,7 @@ void Shell::Init() {
                      base::Unretained(system_tray_delegate_.get()))));
 #endif
 
-  // TODO(oshima): Initialize all RootWindowControllers once, and
-  // initialize controller/delegates above when initializing the
-  // primary root window controller.
-  internal::RootWindowController::CreateForPrimaryDisplay(
-      root_window->GetHost());
-
-  display_controller_->InitSecondaryDisplays();
+  display_controller_->InitDisplays();
 
   // It needs to be created after RootWindowController has been created
   // (which calls OnWindowResized has been called, otherwise the