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

ash/host/ash_window_tree_host.h

Index: ash/host/ash_window_tree_host.h
diff --git a/ash/host/ash_window_tree_host.h b/ash/host/ash_window_tree_host.h
new file mode 100644
index 0000000000000000000000000000000000000000..9962b892835dfa68d6b16d830b0162432d311a3f
--- /dev/null
+++ b/ash/host/ash_window_tree_host.h
@@ -0,0 +1,49 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_HOST_ASH_WINDOW_TREE_HOST_H_
+#define ASH_HOST_ASH_WINDOW_TREE_HOST_H_
+
+#include "ash/ash_export.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace aura {
+class Window;
+class WindowTreeHost;
+}
+
+namespace gfx {
+class Rect;
+}
+
+namespace ash {
+class RootWindowTransformer;
+
+class ASH_EXPORT AshWindowTreeHost {
+ public:
+  // Creates a new AshWindowTreeHost. The caller owns the returned value.
+  static AshWindowTreeHost* Create(const gfx::Rect& initial_bounds);
+
+  virtual ~AshWindowTreeHost() {}
+
+  // Toggles the host's full screen state.
+  virtual void ToggleFullScreen() = 0;
+
+  // Clips the cursor to the bounds of the root window until UnConfineCursor().
+  // We would like to be able to confine the cursor to that window. However,
+  // currently, we do not have such functionality in X. So we just confine
+  // to the root window. This is ok because this option is currently only
+  // being used in fullscreen mode, so root_window bounds = window bounds.
+  virtual bool ConfineCursorToRootWindow() = 0;
+  virtual void UnConfineCursor() = 0;
+
+  virtual void SetRootWindowTransformer(
+      scoped_ptr<RootWindowTransformer> transformer) = 0;
+
+  virtual aura::WindowTreeHost* AsWindowTreeHost() = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_HOST_ASH_WINDOW_TREE_HOST_H_