Oilpan: Remove guardRef and guardDeref from TreeScope.

Source/core/html/canvas/CanvasRenderingContext2D.cpp

Index: Source/core/html/canvas/CanvasRenderingContext2D.cpp
diff --git a/Source/core/html/canvas/CanvasRenderingContext2D.cpp b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
index 8fb31fa2206334a4892cae55288da7a9b2a5c53e..0c9797b0274c72a8c630a6503cc64b08c70528c7 100644
--- a/Source/core/html/canvas/CanvasRenderingContext2D.cpp
+++ b/Source/core/html/canvas/CanvasRenderingContext2D.cpp
@@ -115,9 +115,11 @@ void CanvasRenderingContext2D::unwindStateStack()
 
 CanvasRenderingContext2D::~CanvasRenderingContext2D()
 {
+#if !ENABLE(OILPAN)
 #if !ASSERT_DISABLED
     unwindStateStack();
 #endif
+#endif
 }
 
 bool CanvasRenderingContext2D::isAccelerated() const
@@ -160,6 +162,15 @@ void CanvasRenderingContext2D::restoreContext()
     }
 }
 
+void CanvasRenderingContext2D::trace(Visitor* visitor)
+{
+#if ENABLE(OILPAN)
+    visitor->trace(m_stateStack);
+#endif
+    visitor->trace(m_fetchedFonts);
+    CanvasRenderingContext::trace(visitor);
+}
+
 void CanvasRenderingContext2D::dispatchContextLostEvent(Timer<CanvasRenderingContext2D>*)
 {
     if (contextLostRestoredEventsEnabled()) {