Add a comment that CHECK should not be used until the performance issue is fixed.

third_party/WebKit/Source/wtf/Assertions.h

 /*
  * Copyright (C) 2003, 2006, 2007 Apple Inc.  All rights reserved.
  * 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
@@ skipping 193 matching lines @@
 #else
 #define SECURITY_DCHECK(condition) ((void)0)
 #define SECURITY_CHECK(condition) CHECK(condition)
 #endif
 
 // RELEASE_ASSERT
 // Use in places where failure of an assertion indicates a definite security
 // vulnerability from which execution must not continue even in a release build.
 // Please sure to file bugs for these failures using the security template:
 //    http://code.google.com/p/chromium/issues/entry?template=Security%20Bug
-// RELEASE_ASSERT is deprecated.  We should use CHECK() instead.
+//
+// WARNING: CHECK is slower than RELEASE_ASSERT on MSVC. We should not replace
+// RELEASE_ASSERT with CHECK until the performance issue is fixed
+// (crbug.com/596760).
 #if ENABLE(ASSERT)
 #define RELEASE_ASSERT(assertion) ASSERT(assertion)
 #elif defined(ADDRESS_SANITIZER)
 #define RELEASE_ASSERT(condition) SECURITY_CHECK(condition)
 #else
 #define RELEASE_ASSERT(assertion) \
   (UNLIKELY(!(assertion)) ? (IMMEDIATE_CRASH()) : (void)0)
 #endif
 
 // DEFINE_COMPARISON_OPERATORS_WITH_REFERENCES
@@ skipping 63 matching lines @@
     return static_cast<thisType&>(argument);                                  \
   }                                                                           \
   inline const thisType& to##thisType##OrDie(const argumentType& argument) {  \
     CHECK(referencePredicate);                                                \
     return static_cast<const thisType&>(argument);                            \
   }                                                                           \
   void to##thisType##OrDie(const thisType*);                                  \
   void to##thisType##OrDie(const thisType&)
 
 #endif  // WTF_Assertions_h