Oilpan: fix build after r198049.

Source/modules/mediasession/MediaSession.cpp

Index: Source/modules/mediasession/MediaSession.cpp
diff --git a/Source/modules/mediasession/MediaSession.cpp b/Source/modules/mediasession/MediaSession.cpp
index 644651b5371044e4ba88e6f050e2677b7c1ee60d..0e4483cb78d486789da0ad033e769ace4688e13c 100644
--- a/Source/modules/mediasession/MediaSession.cpp
+++ b/Source/modules/mediasession/MediaSession.cpp
@@ -11,9 +11,9 @@ MediaSession::MediaSession()
 {
 }
 
-RefPtrWillBeRawPtr<MediaSession> MediaSession::create()
+MediaSession* MediaSession::create()
 {
-    return adoptRefWillBeNoop(new MediaSession());
+    return new MediaSession;
 }
 
 void MediaSession::activate()
@@ -24,4 +24,4 @@ void MediaSession::deactivate()
 {
 }
 
-}
+} // namespace blink