Re-introduce the partial magnifier

ash/shell_delegate.h

 // 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_SHELL_DELEGATE_H_
 #define ASH_SHELL_DELEGATE_H_
 
 #include <vector>
 
 #include "ash/ash_export.h"
@@ skipping 131 matching lines @@
 
   // Returns true if spoken feedback is enabled.
   virtual bool IsSpokenFeedbackEnabled() const = 0;
 
   // Invoked to toggle high contrast for accessibility.
   virtual void ToggleHighContrast() = 0;
 
   // Returns true if high contrast mode is enabled.
   virtual bool IsHighContrastEnabled() const = 0;
 
-  // Invoked to change the mode of the screen magnifier.
-  virtual void SetMagnifier(MagnifierType type) = 0;
+  // Invoked to enable the screen magnifier.
+  virtual void SetMagnifierEnabled(bool enabled) = 0;
+
+  // Invoked to change the type of the screen magnifier.
+  virtual void SetMagnifierType(MagnifierType type) = 0;
+
+  // Returns if the screen magnifier is enabled or not.
+  virtual bool IsMagnifierEnabled() const = 0;
 
   // Returns the current screen magnifier mode.
   virtual MagnifierType GetMagnifierType() const = 0;
 
   // Returns true if the user want to show accesibility menu even when all the
   // accessibility features are disabled.
   virtual bool ShouldAlwaysShowAccessibilityMenu() const = 0;
 
   // Invoked to create an AppListViewDelegate. Shell takes the ownership of
   // the created delegate.
@@ skipping 53 matching lines @@
   virtual aura::client::StackingClient* CreateStackingClient() = 0;
 
   // Creates a root window host factory. Shell takes ownership of the returned
   // value.
   virtual RootWindowHostFactory* CreateRootWindowHostFactory() = 0;
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELL_DELEGATE_H_