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

src/assembler.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 1011 matching lines @@
 
   static ExternalReference math_exp_constants(int constant_index);
   static ExternalReference math_exp_log_table();
 
   static ExternalReference page_flags(Page* page);
 
   static ExternalReference ForDeoptEntry(Address entry);
 
   static ExternalReference cpu_features();
 
+  static ExternalReference is_tail_call_elimination_enabled_address(
+      Isolate* isolate);
+
   static ExternalReference debug_is_active_address(Isolate* isolate);
   static ExternalReference debug_after_break_target_address(Isolate* isolate);
 
   static ExternalReference is_profiling_address(Isolate* isolate);
   static ExternalReference invoke_function_callback(Isolate* isolate);
   static ExternalReference invoke_accessor_getter_callback(Isolate* isolate);
 
   static ExternalReference virtual_handler_register(Isolate* isolate);
   static ExternalReference virtual_slot_register(Isolate* isolate);
 
@@ skipping 273 matching lines @@
     std::vector<ConstantPoolEntry> shared_entries;
   };
 
   Label emitted_label_;  // Records pc_offset of emitted pool
   PerTypeEntryInfo info_[ConstantPoolEntry::NUMBER_OF_TYPES];
 };
 
 }  // namespace internal
 }  // namespace v8
 #endif  // V8_ASSEMBLER_H_