[api] Add a switch that controls if ES2015 tail call elimination feature is enabled or not.

include/v8-debug.h

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_V8_DEBUG_H_
 #define V8_V8_DEBUG_H_
 
 #include "v8.h"  // NOLINT(build/include)
 
 /**
@@ skipping 258 matching lines @@
    */
   static void SetLiveEditEnabled(Isolate* isolate, bool enable);
 
   /**
    * Returns array of internal properties specific to the value type. Result has
    * the following format: [<name>, <value>,...,<name>, <value>]. Result array
    * will be allocated in the current context.
    */
   static MaybeLocal<Array> GetInternalProperties(Isolate* isolate,
                                                  Local<Value> value);
+
+  /**
+   * Defines if the ES2015 tail call elimination feature is enabled or not.
+   */
+  static bool IsTailCallEliminationEnabled(Isolate* isolate);
+  static void SetTailCallEliminationEnabled(Isolate* isolate, bool enabled);

[jochen (gone - plz use gerrit), 2016/03/29 15:12:15]

Can you add a comment saying whether this deopts all existing code?

In the future, it might be the case that you can't disable TCO, right? maybe
SetTail... should return a bool indicating whether or not it was indeed
disabled?

or should we just automatically disable TCO if the debugger is engaged?

[Igor Sheludko, 2016/03/29 15:32:19]

1) Probably when we decide to avoid disabling TCO we should remove these
functions from the API.
2) We decided to separate "TCO enabled" from "Debugger is enabled" in order to
let the user debug his code the same way it is run in without debugger. But if
user wants to see less confusing picture it could disable TCO in DevTools.

 };
 
 
 }  // namespace v8
 
 
 #undef EXPORT
 
 
 #endif  // V8_V8_DEBUG_H_