Do not scale ScrollEvent by device scale factor

ash/display/event_transformation_handler.cc

 // Copyright (c) 2013 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/display/event_transformation_handler.h"
 
 #include <cmath>
 
 #include "ash/screen_ash.h"
 #include "ash/shell.h"
@@ skipping 22 matching lines @@
     : transformation_mode_(TRANSFORM_AUTO) {
 }
 
 EventTransformationHandler::~EventTransformationHandler() {
 }
 
 void EventTransformationHandler::OnScrollEvent(ui::ScrollEvent* event) {
   if (transformation_mode_ == TRANSFORM_NONE)
     return;
 
-  // Get the device scale factor and stack it on the final scale factor.
+  // It is unnecessary to scale the event for the device scale factor since
+  // the event locations etc. are already in DIP.
   gfx::Point point_in_screen(event->location());
   aura::Window* target = static_cast<aura::Window*>(event->target());
-  const float scale_at_target = ui::GetDeviceScaleFactor(target->layer());
-  float scale = scale_at_target;
-
-  // Apply some additional scaling if the display is non-integrated.
   wm::ConvertPointToScreen(target, &point_in_screen);
   const gfx::Display& display =
       Shell::GetScreen()->GetDisplayNearestPoint(point_in_screen);
+
+  // Apply some additional scaling if the display is non-integrated.
   if (!display.IsInternal())
-    scale *= kBoostForNonIntegrated;
-
-  event->Scale(scale);
+    event->Scale(kBoostForNonIntegrated);
 }
 
 #if defined(OS_CHROMEOS)
 // This is to scale the TouchEvent's radius when the touch display is in
 // mirror mode. TouchEvent's radius is often reported in the touchscreen's
 // native resolution. In mirror mode, the touch display could be configured
 // at a lower resolution. We scale down the radius using the ratio defined as
 // the sqrt of
 // (mirror_width * mirror_height) / (native_width * native_height)
 void EventTransformationHandler::OnTouchEvent(ui::TouchEvent* event) {
@@ skipping 22 matching lines @@
   }
 
   float area_ratio_sqrt = std::sqrt(area_ratio_map.begin()->second);
   event->set_radius_x(event->radius_x() * area_ratio_sqrt);
   event->set_radius_y(event->radius_y() * area_ratio_sqrt);
 }
 #endif  // defined(OS_CHROMEOS)
 
 }  // namespace internal
 }  // namespace ash