Full-screen Magnifier: Support warping the cursor on the edge

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 4731c74c939b8421cdb0f63305c6dfb268695dc5..e990059ca1ec930006d36c3f02a15cad97c21508 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -753,7 +753,9 @@ void Shell::Init() {
   AddRootWindowEventFilter(tooltip_controller_.get());
 
   drag_drop_controller_.reset(new internal::DragDropController);
-  magnification_controller_.reset(new internal::MagnificationController);
+  magnification_controller_.reset(
+      internal::MagnificationController::CreateInstance());
+  AddRootWindowEventFilter(magnification_controller_.get());
   power_button_controller_.reset(new PowerButtonController);
   AddShellObserver(power_button_controller_.get());
   video_detector_.reset(new VideoDetector);