Remove unnecesary usage of RefPtr and PassRefPtr of DatabaseContext.

Source/modules/webdatabase/DatabaseContext.cpp

Index: Source/modules/webdatabase/DatabaseContext.cpp
diff --git a/Source/modules/webdatabase/DatabaseContext.cpp b/Source/modules/webdatabase/DatabaseContext.cpp
index 250260a7f22f0a20bccbe0dd5648435ca133c377..e42cf4a89193efdc4de30cd8a90bd8a10c272264 100644
--- a/Source/modules/webdatabase/DatabaseContext.cpp
+++ b/Source/modules/webdatabase/DatabaseContext.cpp
@@ -144,10 +144,9 @@ void DatabaseContext::stop()
     stopDatabases();
 }
 
-PassRefPtr<DatabaseContext> DatabaseContext::backend()
+DatabaseContext* DatabaseContext::backend()
 {
-    DatabaseContext* backend = static_cast<DatabaseContext*>(this);
-    return backend;
+    return this;
 }
 
 DatabaseThread* DatabaseContext::databaseThread()