Fix clang-cl release component build failure on windows.

third_party/WebKit/Source/core/frame/UseCounter.h

Index: third_party/WebKit/Source/core/frame/UseCounter.h
diff --git a/third_party/WebKit/Source/core/frame/UseCounter.h b/third_party/WebKit/Source/core/frame/UseCounter.h
index 952d9c884b6a5392acd48b2f1b076c4679cc22cc..d82e13ee983f623c873b20e75016af68bde26a46 100644
--- a/third_party/WebKit/Source/core/frame/UseCounter.h
+++ b/third_party/WebKit/Source/core/frame/UseCounter.h
@@ -1359,7 +1359,7 @@ private:
 
     // 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();