Add the partial screen magnifier to Chrome OS.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index e0c0cae7526975a51e9a6b97a4d0b4dda6f631e3..b3d60e4acbda98cbbd5f552bd038b7163c4028cd 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -89,6 +89,7 @@ class MouseCursorEventFilter;
 class OutputConfiguratorAnimation;
 class OverlayEventFilter;
 class PanelLayoutManager;
+class PartialMagnificationController;
 class ResizeShadowController;
 class RootWindowController;
 class RootWindowLayoutManager;
@@ -300,6 +301,10 @@ class ASH_EXPORT Shell : ash::CursorDelegate {
     return magnification_controller_.get();
   }
 
+  internal::PartialMagnificationController* partial_magnification_controller() {
+    return partial_magnification_controller_.get();
+  }
+
   Launcher* launcher() { return launcher_.get(); }
 
   const ScreenAsh* screen() { return screen_; }
@@ -439,6 +444,8 @@ class ASH_EXPORT Shell : ash::CursorDelegate {
   scoped_ptr<DisplayController> display_controller_;
   scoped_ptr<HighContrastController> high_contrast_controller_;
   scoped_ptr<internal::MagnificationController> magnification_controller_;
+  scoped_ptr<internal::PartialMagnificationController>
+      partial_magnification_controller_;
   scoped_ptr<aura::FocusManager> focus_manager_;
   scoped_ptr<aura::client::UserActionClient> user_action_client_;
   scoped_ptr<internal::MouseCursorEventFilter> mouse_cursor_filter_;