Oilpan: add transition types to FileSystem APIs.

Source/modules/filesystem/FileWriterBase.h

Index: Source/modules/filesystem/FileWriterBase.h
diff --git a/Source/modules/filesystem/FileWriterBase.h b/Source/modules/filesystem/FileWriterBase.h
index 8cf9b87c0dfa8e6a7c01689b25c508f9ceef0cd4..d9202de8c759298fe7193fa3e11ee01779a0c8f0 100644
--- a/Source/modules/filesystem/FileWriterBase.h
+++ b/Source/modules/filesystem/FileWriterBase.h
@@ -31,6 +31,7 @@
 #ifndef FileWriterBase_h
 #define FileWriterBase_h
 
+#include "heap/Handle.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/RefCounted.h"
@@ -39,7 +40,7 @@ namespace blink { class WebFileWriter; }
 
 namespace WebCore {
 
-class FileWriterBase : public RefCounted<FileWriterBase> {
+class FileWriterBase : public RefCountedWillBeRefCountedGarbageCollected<FileWriterBase> {
 public:
     virtual ~FileWriterBase();
     void initialize(PassOwnPtr<blink::WebFileWriter>, long long length);
@@ -53,6 +54,8 @@ public:
         return m_length;
     }
 
+    virtual void trace(Visitor*) { }
+
 protected:
     FileWriterBase();