Oilpan: fix build after r198049.

Source/modules/mediasession/MediaSession.h

Index: Source/modules/mediasession/MediaSession.h
diff --git a/Source/modules/mediasession/MediaSession.h b/Source/modules/mediasession/MediaSession.h
index e7dd0cf5c4f7ac856ce34697f86d8c662213656c..45ead4758948a136bf46414b8f7a8a7b6133496f 100644
--- a/Source/modules/mediasession/MediaSession.h
+++ b/Source/modules/mediasession/MediaSession.h
@@ -10,18 +10,20 @@
 
 namespace blink {
 
-class MediaSession : public ScriptWrappable, public RefCountedWillBeNoBase<MediaSession> {
+class MediaSession : public GarbageCollected<MediaSession>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    static RefPtrWillBeRawPtr<MediaSession> create();
+    static MediaSession* create();
 
     void activate();
     void deactivate();
 
+    DEFINE_INLINE_TRACE() { }
+
 private:
     MediaSession();
 };
 
-}
+} // namespace blink
 
 #endif // MediaSession_h