Allow assertions to be enabled in Blink Release builds.

public/web/WebScopedMicrotaskSuppression.h

 /*
  * Copyright (C) 2012 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 45 matching lines @@
 //
 class WebScopedMicrotaskSuppression {
 public:
     WebScopedMicrotaskSuppression() { initialize(); }
     ~WebScopedMicrotaskSuppression() { reset(); }
 
 private:
     BLINK_EXPORT void initialize();
     BLINK_EXPORT void reset();
 
-#ifndef NDEBUG
+    // Always declare this data member. When assertions are on in
+    // Release builds of Blink, this header may be included from
+    // Chromium with different preprocessor options than used when
+    // building Blink itself.
     class Impl;
     WebPrivateOwnPtr<Impl> m_impl;
-#endif
 };
 
 } // WebKit
 
 #endif