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

src/x64/builtins-x64.cc

Index: src/x64/builtins-x64.cc
diff --git a/src/x64/builtins-x64.cc b/src/x64/builtins-x64.cc
index 2c772995b86f2c8ceab4e6fddd50fd535cec1050..316378348c20fdb37668f50af1a482fd051f153e 100644
--- a/src/x64/builtins-x64.cc
+++ b/src/x64/builtins-x64.cc
@@ -2052,6 +2052,15 @@ void PrepareForTailCall(MacroAssembler* masm, Register args_reg,
   DCHECK(!AreAliased(args_reg, scratch1, scratch2, scratch3));
   Comment cmnt(masm, "[ PrepareForTailCall");
 
+  // Prepare for tail call only if ES2015 tail call elimination is active.
+  Label done;
+  ExternalReference is_tail_call_elimination_enabled =
+      ExternalReference::is_tail_call_elimination_enabled_address(
+          masm->isolate());
+  __ Move(kScratchRegister, is_tail_call_elimination_enabled);
+  __ cmpb(Operand(kScratchRegister, 0), Immediate(0));
+  __ j(equal, &done);
+
   // Drop possible interpreter handler/stub frame.
   {
     Label no_interpreter_frame;
@@ -2091,6 +2100,7 @@ void PrepareForTailCall(MacroAssembler* masm, Register args_reg,
   ParameterCount callee_args_count(args_reg);
   __ PrepareForTailCall(callee_args_count, caller_args_count_reg, scratch2,
                         scratch3, ReturnAddressState::kOnStack);
+  __ bind(&done);
 }
 }  // namespace