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

src/external-reference-table.cc

Index: src/external-reference-table.cc
diff --git a/src/external-reference-table.cc b/src/external-reference-table.cc
index b68b5f5e9d445de7ed388c9e6f0ee08f50d94140..e6d5bf13da16a3cda77e78ac00f49e292e8d917f 100644
--- a/src/external-reference-table.cc
+++ b/src/external-reference-table.cc
@@ -172,6 +172,9 @@ ExternalReferenceTable::ExternalReferenceTable(Isolate* isolate) {
       "Isolate::virtual_slot_register()");
   Add(ExternalReference::runtime_function_table_address(isolate).address(),
       "Runtime::runtime_function_table_address()");
+  Add(ExternalReference::is_tail_call_elimination_enabled_address(isolate)
+          .address(),
+      "Isolate::is_tail_call_elimination_enabled_address()");
 
   // Debug addresses
   Add(ExternalReference::debug_after_break_target_address(isolate).address(),