Add the partial screen magnifier to Chrome OS.

ash/magnifier/partial_magnification_controller.h

Index: ash/magnifier/partial_magnification_controller.h
diff --git a/ash/magnifier/partial_magnification_controller.h b/ash/magnifier/partial_magnification_controller.h
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+// Copyright (c) 2012 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_MAGNIFIER_PARTIAL_MAGNIFICATION_CONTROLLER_H_
+#define ASH_MAGNIFIER_PARTIAL_MAGNIFICATION_CONTROLLER_H_
+
+namespace aura {
+class RootWindow;
+}
+
+namespace ash {
+namespace internal {
+
+const float kDefaultPartialMagnifiedScale = 1.5f;
+const float kNonPartialMagnifiedScale = 1.0f;
+
+// Controls the partial screen magnifier, which is a small area of the screen
+// which is zoomed in.  The zoomed area follows the mouse cursor when enabled.
+class PartialMagnificationController {
+ public:
+  virtual ~PartialMagnificationController() {}
+
+  // Creates a new PartialMagnificationController. The caller takes ownership
+  // of the returned object.
+  static PartialMagnificationController* CreateInstance();
+
+  // Enables (or disables if |enabled| is false) partial screen magnifier
+  // feature.
+  virtual void SetEnabled(bool enabled) = 0;
+
+  virtual bool IsEnabled() = 0;
+
+  // Sets the magnification ratio. 1.0f means no magnification.
+  virtual void SetScale(float scale) = 0;
+  // Returns the current magnification ratio.
+  virtual float GetScale() const = 0;
+
+ protected:
+  PartialMagnificationController() {}
+};
+
+}  // namespace internal
+}  // namespace ash
+
+#endif  // ASH_MAGNIFIER_PARTIAL_MAGNIFICATION_CONTROLLER_H_