Create libsampler as V8 sampler library.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 83b777d30948104bec43ba3c9926cd68ff637690..3597b31b85a6cba555b0cc6b9ac13d12be4ade25 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -6296,6 +6296,11 @@ class V8_EXPORT Isolate {
    */
   void VisitWeakHandles(PersistentHandleVisitor* visitor);
 
+  /**
+   * Check if this isolate is in use.

[alph, 2016/05/03 18:48:07]

The description doesn't add much information to the function name. Could you
write more detailed info on what 'in use' means.

[lpy, 2016/05/04 00:09:23]

Done.

+   */
+  bool IsInUse();
+
  private:
   template <class K, class V, class Traits>
   friend class PersistentValueMapBase;