Revert of Remove obsolete JSFunction::IsOptimizable predicate.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 9b43b9d101be483af982768b8747f1c5126924ac..2889259822bd69dc3960202dd7b4a57b4c701dd6 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -7588,6 +7588,9 @@
   // Tells whether or not this function has been optimized.
   inline bool IsOptimized();
 
+  // Tells whether or not this function can be optimized.
+  inline bool IsOptimizable();
+
   // Mark this function for lazy recompilation. The function will be
   // recompiled the next time it is executed.
   void MarkForOptimization();