Allow assertions to be enabled in Blink Release builds.

Source/wtf/WeakPtr.h

 /*
  * 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:
  * 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 39 matching lines @@
 
     void clear()
     {
         ASSERT(m_boundThread == currentThread());
         m_ptr = 0;
     }
 
     void bindTo(T* ptr)
     {
         ASSERT(!m_ptr);
-#ifndef NDEBUG
+#if ENABLE(ASSERT)
         m_boundThread = currentThread();
 #endif
         m_ptr = ptr;
     }
 
 private:
     WeakReference() : m_ptr(0) { }
 
     explicit WeakReference(T* ptr)
         : m_ptr(ptr)
-#ifndef NDEBUG
+#if ENABLE(ASSERT)
         , m_boundThread(currentThread())
 #endif
     {
     }
 
     T* m_ptr;
-#ifndef NDEBUG
+#if ENABLE(ASSERT)
     ThreadIdentifier m_boundThread;
 #endif
 };
 
 template<typename T>
 class WeakPtr {
     WTF_MAKE_FAST_ALLOCATED;
 public:
     WeakPtr() { }
     WeakPtr(std::nullptr_t) { }
@@ skipping 55 matching lines @@
     RefPtr<WeakReference<T> > m_ref;
 };
 
 } // namespace WTF
 
 using WTF::WeakPtr;
 using WTF::WeakPtrFactory;
 using WTF::WeakReference;
 
 #endif