events: Make sure the unaccelerated scroll deltas get adjusted properly for device-scale-factor.

ui/base/events/event.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 "ui/base/events/event.h"
 
 #if defined(USE_X11)
 #include <X11/Xlib.h>
 #endif
 
@@ skipping 661 matching lines @@
   CHECK(IsScrollEvent());
 }
 
 void ScrollEvent::Scale(const float factor) {
   x_offset_ *= factor;
   y_offset_ *= factor;
   x_offset_ordinal_ *= factor;
   y_offset_ordinal_ *= factor;
 }
 
+void ScrollEvent::UpdateForRootTransform(const gfx::Transform& root_transform) {
+  LocatedEvent::UpdateForRootTransform(root_transform);
+  gfx::DecomposedTransform decomp;
+  bool success = gfx::DecomposeTransform(&decomp, root_transform);
+  DCHECK(success);
+  if (decomp.scale[0])
+    x_offset_ordinal_ /= decomp.scale[0];
+  if (decomp.scale[1])
+    y_offset_ordinal_ /= decomp.scale[1];
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // GestureEvent
 
 GestureEvent::GestureEvent(EventType type,
                            int x,
                            int y,
                            int flags,
                            base::TimeDelta time_stamp,
                            const GestureEventDetails& details,
                            unsigned int touch_ids_bitfield)
@@ skipping 12 matching lines @@
 int GestureEvent::GetLowestTouchId() const {
   if (touch_ids_bitfield_ == 0)
     return -1;
   int i = -1;
   // Find the index of the least significant 1 bit
   while (!(1 << ++i & touch_ids_bitfield_));
   return i;
 }
 
 }  // namespace ui