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 a2c331879613a4a8a33fd2af8f564c1b2e132949..fa54bae867aa8a41a75e61f543935d13f5e58af8 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()) {