Fix clang-cl release component build failure on windows.

third_party/WebKit/Source/core/frame/UseCounter.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:
  * 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 1341 matching lines @@
 
     unsigned m_muteCount;
     Context m_context;
 
     // Track what features/properties have been reported to the (non-legacy) histograms.
     BitVector m_featuresRecorded;
     BitVector m_CSSRecorded;
 
     // Encapsulates the work to preserve the old "FeatureObserver" histogram with original semantics
     // TODO(rbyers): remove this - http://crbug.com/597963
-    class LegacyCounter {
+    class CORE_EXPORT LegacyCounter {
     public:
         LegacyCounter();
         ~LegacyCounter();
         void countFeature(Feature);
         void countCSS(CSSPropertyID);
         void updateMeasurements();
     private:
         // Tracks what features/properties need to be reported to the legacy histograms.
         BitVector m_featureBits;
         BitVector m_CSSBits;
     } m_legacyCounter;
 };
 
 } // namespace blink
 
 #endif // UseCounter_h