Oilpan: add missing leftmost trace()s for GC mixins.

Source/web/DatabaseClientImpl.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 29 matching lines @@
 
 PassOwnPtrWillBeRawPtr<DatabaseClientImpl> DatabaseClientImpl::create()
 {
     return adoptPtrWillBeNoop(new DatabaseClientImpl());
 }
 
 DatabaseClientImpl::~DatabaseClientImpl()
 {
 }
 
+void DatabaseClientImpl::trace(Visitor* visitor)
+{
+    DatabaseClient::trace(visitor);
+}
+
 bool DatabaseClientImpl::allowDatabase(ExecutionContext* executionContext, const String& name, const String& displayName, unsigned long estimatedSize)
 {
     ASSERT(executionContext->isContextThread());
     Document* document = toDocument(executionContext);
     WebLocalFrameImpl* webFrame = WebLocalFrameImpl::fromFrame(document->frame());
     if (!webFrame)
         return false;
     if (webFrame->permissionClient())
         return webFrame->permissionClient()->allowDatabase(name, displayName, estimatedSize);
     return true;
 }
 
 DatabaseClientImpl::DatabaseClientImpl()
 {
 }
 
 } // namespace blink