Use refs for non-null GraphicsContext, Scrollbar, etc. in scrollbar related code

third_party/WebKit/Source/core/html/shadow/SpinButtonElement.cpp

 /*
  * Copyright (C) 2006, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 198 matching lines @@
 }
 
 bool SpinButtonElement::matchesReadWritePseudoClass() const
 {
     return shadowHost()->matchesReadWritePseudoClass();
 }
 
 void SpinButtonElement::startRepeatingTimer()
 {
     m_pressStartingState = m_upDownState;
-    ScrollbarTheme* theme = ScrollbarTheme::theme();
-    m_repeatingTimer.start(theme->initialAutoscrollTimerDelay(), theme->autoscrollTimerDelay(), BLINK_FROM_HERE);
+    ScrollbarTheme& theme = ScrollbarTheme::theme();
+    m_repeatingTimer.start(theme.initialAutoscrollTimerDelay(), theme.autoscrollTimerDelay(), BLINK_FROM_HERE);
 }
 
 void SpinButtonElement::stopRepeatingTimer()
 {
     m_repeatingTimer.stop();
 }
 
 void SpinButtonElement::step(int amount)
 {
     if (!shouldRespondToMouseEvents())
@@ skipping 26 matching lines @@
     return !m_spinButtonOwner || m_spinButtonOwner->shouldSpinButtonRespondToMouseEvents();
 }
 
 DEFINE_TRACE(SpinButtonElement)
 {
     visitor->trace(m_spinButtonOwner);
     HTMLDivElement::trace(visitor);
 }
 
 }