Make zoom filter independent of the layer size.

ash/magnifier/partial_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/partial_magnification_controller.h"
 
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
 #include "ui/aura/root_window.h"
 #include "ui/views/corewm/compound_event_filter.h"
@@ skipping 143 matching lines @@
   zoom_widget_->Show();
 
   aura::Window* window = zoom_widget_->GetNativeView();
   window->SetName(kPartialMagniferWindowName);
 
   zoom_widget_->GetNativeView()->layer()->SetBounds(
       gfx::Rect(0, 0,
                 kMagnifierWidth,
                 kMagnifierHeight));
   zoom_widget_->GetNativeView()->layer()->SetBackgroundZoom(
-      (kMagnifierWidth - (kMagnifierWidth / scale_)) / 2,
-      (kMagnifierHeight - (kMagnifierHeight / scale_)) / 2,
       scale_,
       kZoomInset);
 
   zoom_widget_->AddObserver(this);
 }
 
 void PartialMagnificationController::CloseMagnifierWindow() {
   if (zoom_widget_) {
     RemoveZoomWidgetObservers();
     zoom_widget_->Close();
@@ skipping 28 matching lines @@
        iter != root_windows.end(); ++iter) {
     aura::RootWindow* root_window = *iter;
     if (root_window->ContainsPointInRoot(
             root_window->GetLastMouseLocationInRoot()))
       return root_window;
   }
   return NULL;
 }
 
 }  // namespace ash