Magnifier: Prevent useless operation in enabling/disabling magnifier.

ash/magnifier/magnification_controller.cc

 // 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.
 
 #include "ash/magnifier/magnification_controller.h"
 
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/system/tray/system_tray_delegate.h"
 #include "ui/aura/client/cursor_client.h"
@@ skipping 454 matching lines @@
 void MagnificationControllerImpl::EnsurePointIsVisible(
     const gfx::Point& point,
     bool animate) {
   if (!is_enabled_)
     return;
 
   EnsurePointIsVisibleWithScale(point, scale_, animate);
 }
 
 void MagnificationControllerImpl::SetEnabled(bool enabled) {
+  if (enabled == is_enabled_)
+    return;
+
   if (enabled) {
     float scale =
         ash::Shell::GetInstance()->delegate()->GetSavedScreenMagnifierScale();
     if (scale <= 0.0f)
       scale = GetDefaultZoomScale();
     ValidateScale(&scale);
     RedrawKeepingMousePosition(scale, true);
     is_enabled_ = enabled;
   } else {
     RedrawKeepingMousePosition(kNonMagnifiedScale, true);
@@ skipping 48 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationController:
 
 // static
 MagnificationController* MagnificationController::CreateInstance() {
   return new MagnificationControllerImpl();
 }
 
 }  // namespace ash