Oilpan: fix compilation after r178648.

Source/core/html/canvas/WebGLFramebuffer.cpp

 /*
  * Copyright (C) 2009 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 612 matching lines @@
     ASSERT(index >= 0);
     if (index < static_cast<int>(m_drawBuffers.size()))
         return m_drawBuffers[index];
     if (drawBuffer == GL_DRAW_BUFFER0_EXT)
         return GL_COLOR_ATTACHMENT0;
     return GL_NONE;
 }
 
 void WebGLFramebuffer::trace(Visitor* visitor)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_attachments);
+#endif
     WebGLContextObject::trace(visitor);
 }
 
 }