[Ozone] Check valid GetFlingData parameters before writing to them

ui/events/ozone/events_ozone.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 "ui/events/event.h"
 #include "ui/events/event_constants.h"
 #include "ui/events/event_utils.h"
 
 namespace ui {
 
@@ skipping 126 matching lines @@
 
 bool GetFlingData(const base::NativeEvent& native_event,
                   float* vx,
                   float* vy,
                   float* vx_ordinal,
                   float* vy_ordinal,
                   bool* is_cancel) {
   const ui::ScrollEvent* event =
       static_cast<const ui::ScrollEvent*>(native_event);
   DCHECK(event->IsScrollEvent());
-  *vx = event->x_offset();
-  *vy = event->y_offset();
-  *vx_ordinal = event->x_offset_ordinal();
-  *vy_ordinal = event->y_offset_ordinal();
-  *is_cancel = event->type() == ET_SCROLL_FLING_CANCEL;
+  if (vx)
+    *vx = event->x_offset();
+  if (vy)
+    *vy = event->y_offset();
+  if (vx_ordinal)
+    *vx_ordinal = event->x_offset_ordinal();
+  if (vy_ordinal)
+    *vy_ordinal = event->y_offset_ordinal();
+  if (is_cancel)
+    *is_cancel = event->type() == ET_SCROLL_FLING_CANCEL;
+
   return true;
 }
 
 int GetModifiersFromKeyState() {
   NOTIMPLEMENTED();
   return 0;
 }
 
 }  // namespace ui