Oilpan: switch some leftover raw references over to traced Member<>s.

Source/modules/filesystem/DOMFileSystemBase.cpp

Index: Source/modules/filesystem/DOMFileSystemBase.cpp
diff --git a/Source/modules/filesystem/DOMFileSystemBase.cpp b/Source/modules/filesystem/DOMFileSystemBase.cpp
index 87ca2b99904084719a83bc4160361b4e4a36dbd5..ecb466da8f850f6e5c473161bb3e007fa85fe39e 100644
--- a/Source/modules/filesystem/DOMFileSystemBase.cpp
+++ b/Source/modules/filesystem/DOMFileSystemBase.cpp
@@ -74,6 +74,11 @@ DOMFileSystemBase::~DOMFileSystemBase()
 {
 }
 
+DEFINE_TRACE(DOMFileSystemBase)
+{
+    visitor->trace(m_context);
+}
+
 WebFileSystem* DOMFileSystemBase::fileSystem() const
 {
     Platform* platform = Platform::current();