[es6] Add a flag to the Isolate that defines whether ES2015 tail call elimination is enabled or not.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 957115d1c27edff774df73978bd5c8bbf8282abb..1ebaa28a76022352a799019e89d1cf2eed0498d1 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -1089,6 +1089,16 @@ class Isolate {
   int GetNextUniqueSharedFunctionInfoId() { return next_unique_sfi_id_++; }
 #endif
 
+  // Support for dynamically disabling tail call elimination.
+  Address is_tail_call_elimination_enabled_address() {
+    return reinterpret_cast<Address>(&is_tail_call_elimination_enabled_);
+  }
+  bool is_tail_call_elimination_enabled() const {
+    return is_tail_call_elimination_enabled_;
+  }
+  void set_tail_call_elimination_enabled(bool enabled) {
+    is_tail_call_elimination_enabled_ = enabled;
+  }
 
   void AddDetachedContext(Handle<Context> context);
   void CheckDetachedContextsAfterGC();
@@ -1277,6 +1287,9 @@ class Isolate {
   // True if this isolate was initialized from a snapshot.
   bool initialized_from_snapshot_;
 
+  // True if ES2015 tail call elimination feature is enabled.
+  bool is_tail_call_elimination_enabled_;
+
   // Time stamp at initialization.
   double time_millis_at_init_;