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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index 0000000000000000000000000000000000000000..cf8c7044018499f7f0d6f52bd480b3a4acd4ea21
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+++ b/ash/magnifier/partial_magnification_controller.h
@@ -0,0 +1,47 @@
+// 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 {

[sky, 2012/10/11 17:00:49]

Is there a reason to make this pure virtual?

[Zachary Kuznia, 2012/10/12 08:41:35]

It's done this way in order to match the style of magnification_controller.h

[sky, 2012/10/12 17:09:19]

Is there a reason for that?

[Zachary Kuznia, 2012/10/15 08:28:40]

Apparently the reason was to keep the header file simpler.  Would you prefer if
I eliminated the pure virtual interface?

+ 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() const = 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_