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

ash/host/transformer_helper.h

Index: ash/host/transformer_helper.h
diff --git a/ash/host/transformer_helper.h b/ash/host/transformer_helper.h
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+++ b/ash/host/transformer_helper.h
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+// 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_TRANSFORMER_HELPER_H_
+#define ASH_HOST_TRANSFORMER_HELPER_H_
+
+#include "base/memory/scoped_ptr.h"
+
+namespace gfx {
+class Insets;
+class Size;
+class Transform;
+}
+
+namespace ash {
+class AshWindowTreeHost;
+class RootWindowTransformer;
+
+// A helper class to handle ash specific feature that requires
+// transforming a root window (such as rotation, UI zooming).
+class TransformerHelper {
+ public:
+  explicit TransformerHelper(AshWindowTreeHost* ash_host);
+  ~TransformerHelper();
+
+  // Returns the the insets that specifies the effective root window
+  // area within the host window.
+  gfx::Insets GetHostInsets() const;
+
+  // Sets a simple transform with no host insets.
+  void SetTransform(const gfx::Transform& transform);
+
+  // Sets a RootWindowTransformer which takes the insets into account.
+  void SetRootWindowTransformer(scoped_ptr<RootWindowTransformer> transformer);
+
+  // Returns the transforms applied to the root window.
+  gfx::Transform GetTransform() const;
+  gfx::Transform GetInverseTransform() const;
+
+  // Updates the root window size based on the host size and
+  // current transform.
+  void UpdateWindowSize(const gfx::Size& host_size);
+
+ private:
+  AshWindowTreeHost* ash_host_;
+  scoped_ptr<RootWindowTransformer> transformer_;
+
+  DISALLOW_COPY_AND_ASSIGN(TransformerHelper);
+};
+
+}  // namespace ash
+
+#endif  // ASH_HOST_TRANSFORMER_HELPER_H_