Create libsampler as V8 sampler library.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 52b6192b87643bec0a0abff62dac9864da01baf7..a5e341ca6fe4c6f8057ce34f4526ec48dd2bc6e8 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -6285,6 +6285,12 @@ class V8_EXPORT Isolate {
    */
   void VisitWeakHandles(PersistentHandleVisitor* visitor);
 
+  /**
+   * Check if this isolate is in use.
+   * True if at least one thread Enter'ed this isolate.
+   */
+  bool IsInUse();
+
  private:
   template <class K, class V, class Traits>
   friend class PersistentValueMapBase;